Who in European space will ask the impertinent question: How much would it cost to add a second Vulcain to the Ariane 5/6?

 Copyright 2023 Robert Clark

 

ArianeSpace Needs to Transition to Reusability to Survive.

 European space advocates have been lamenting that there seems to be no near term route to keeping up with SpaceX, getting reusable launchers, and towards achieving manned space flight. However, in point of fact ESA already has the components to form a launcher comparable to the Falcon 9 and at lower price, while keeping pace with SpaceX in reusability, and in manned spaceflight.

 All it would require is someone, anyone in the Europeans space community to ask the impertinent question, "How much would it cost to add a 2nd Vulcain to the Ariane 5/6?"

  For once that question is asked, and ArianeSpace forced to answer honestly, they would have to admit it could be done for only a development cost in the range of only ~$200 million. But then it would become obvious how to proceed.

 First, note that the Ariane 6 that was planned to compete with the SpaceX Falcon 9 has been pushed back to 2024, when its original launch date was in 2020, extending the time where SpaceX is cornering the market. Note also the Ariane 6 will not be reusable. In fact ArianeSpace has admitted they won't be fielding a reusable launcher until the 2030's. 

 ULA was driven to the brink of bankruptcy by denying the importance of reusability. There is little doubt the same will happen to ArianeSpace if they wait a decade to field a reusable vehicle. Independent European space observers have also made this point about the choice of the non-reusable Ariane 6:

Europe’s lack of rocket ‘audacity’ leaves it scrambling in the space race
European policymakers want to stop SpaceX from dominating the launch market.
BY JOSHUA POSANER
JANUARY 15, 2021 12:28 PM CET 6 MINUTES READ
That 2014 decision haunts French Economy Minister Bruno Le Maire, who keeps a warning of that moment on his desk.
“The European space adventure is magnificent, but in 2014 there was a fork in the road, and we didn’t take the right path,” Le Maire told a conference last September. “We should have made the choice of the reusable launcher. We should have had this audacity.”
https://www.politico.eu/article/europe-arianespace-rocket-space-race/

 The Fast Route to Reusability.

 The problem with reusability for the Ariane 5 and 6 is they use solids for a large portion of their takeoff thrust. These large side boosters also make up a large portion of the cost. In fact, the situation has actually gotten worse with the Ariane 6. But the Space Shuttle program demonstrated you don't save on reuse with solid side boosters. By the time you fish the SRB's out of the ocean, tow them to port, transport them from port back to the manufacturing facility, clean them out from all the burnt on combustion products, and then finally refill them with propellant, the cost is no better than just using new ones to begin with. A little thought makes it easy to see why. Solid side boosters are just a filled in metal pipe. The cost of that metal pipe is small compared to all the processing involved in making the SRB. Keeping the same metal pipe but increasing all the needed steps for processing does not reduce the cost of the SRB.

 So to get the low cost reusable rocket you have to dispense with the SRB's. Necessarily that means you have to use additional liquid-fueled core engines. Then is adding an additional core engine a multi-billion dollar, or euro, development? 

 No! I was quite startled to find JAXA was able to add an additional hydrolox engine to the H-II first stage for only an approx. $200 million development cost.

 See the highlighted passage in this article where the cost to add another engine to the H-II was only 27 billion Yen, about $200 million: 

 

 But that means instead of the multi-billion current development cost of the Ariane 6, the same could have been accomplished for just a few hundred million and would also have been reusable! I made this point here:

Multi-Vulcain Ariane 6.

https://exoscientist.blogspot.com/2018/02/multi-vulcain-ariane-6.html

 Thus the importance of asking that impertinent question of ArianeSpace, "How much to add an additional Vulcain to the Ariane 5/6?"

WHY Are the Far More Expensive SRB's Used Rather then the Cheaper Liquid-fueled Engines? 

 Knowledgeable ESA observers have been aware for awhile now that the ESA policies for distributing funds and costs to the differing member states do not result in the most cost effective vehicles. It’s a policy called geographical-return that requires member states costs to be apportioned by some set proportion of the billion dollar development costs. So if some member states have been contributing some large proportion of the costs through solid side boosters, that cost continues to be part of the development for new rockets or upgrades.

 The governments of the member states regard this as a good thing because it helps to keep active, and paid, the space industries and space industry employees in their countries. But another key reason why some member states like the funds for the ESA to go to develop solid rocket side boosters is because those funds help also to develop solid rockets for their defense programs. So rather than those countries having to pay the entire cost of the solid rocket missiles in their defense programs on their own, some portion of that is actually paid for by the ESA in developing solid rocket side boosters for space launchers.

 You can see why there is a great incentive for those member states, which have great influence on the direction and funding choices for the ESA, to continue to want to use solid rocket boosters in all launchers produced by the ESA.

 But the stunning fact is how much more expensive the solids are for the Ariane 6 than just adding another Vulcain engine! The latest cost figures for the Ariane 6 are the €75M for the two SRB version and €115M for the four SRB version. 

 This suggests, as a first order estimate, that we can take the cost of two SRB’s as €40M. But the cost of a single Vulcan is only €10 million! So the two SRB’s on the Ariane 6 base version costs 4 times more than an additional Vulcain! Therefore, again as a first order estimate, we can take the cost of a two Vulcain Ariane 6 with no SRB’s as only €45 million, ~$50 million. This compares quite favorably to current $67 million cost of the Falcon 9.

 The reason why this isn’t done can not be attributed to some supposed multi-billion development cost to add an additional Vulcain to the Ariane core. Actually, it’s the current plan for the Ariane 6 with the newly developed solids, new upper stage, and new Vinci engine whose development cost is in the $4+ billion range. It’s really quite stunning to realize the same could have been accomplished at only a ~$200 development cost simply by adding another Vulcain to the Ariane 5 core, using the same original cryogenic upper stage. Nearly a factor of 20 times cheaper!

 But nobody knows this because nobody asks that one simple question, “How much would it cost to add a second Vulcain to the Ariane 5/6?”

 Now, once you have the all-liquid Ariane 6 that costs even cheaper than the Falcon 9, you can also keep up with SpaceX in reducing price by reusability by also reusing the core stage via powered landing a la the F9 booster. Again, the solids in the current Ariane 6 version would not save on reusing them as the Space Shuttle program abundantly showed. So that huge €40 million cost just for the SRB’s on the Ariane 6(more than the cost of the entire rest of the rocket!) out of the total  €75 million would be fixed no matter how many times you wanted to reuse the core.

 It might be argued that even a fully throttled down single Vulcain would have too much thrust for a hovering landing. Actually, this is the case also with the Falcon 9. It uses what SpaceX calls "hover-slam" for landing. The thrust is precisely timed so the booster just reaches 0 velocity as it touches down. Actually, I'm not a fan of "hover-slam". Much better for the Ariane case would be to use two Vinci engines for the landing only. It is designed to be air-startable and restartable. It weighs without the nozzle extension for vacuum use only 160 kg. So two would weigh only 320kg on the first stage. It's use would allow true hovering landing for the first stage.

Three Vulcains on the Ariane 5/6 Match the Falcon 9 in Payload at a Lower Price.

 The two Vulcain Ariane 5/6 would have lower payload than the Falcon 9. But it would be quite competitive for the lucrative geosynchronous transfer orbit(GTO) used by many communications satellites, at ~6,000 kg to GTO at lower price than the F9. The F9 is at about 8,000 kg to GTO. But most satellites don't need this full capacity anyway.

 However, if we used three Vulcains we could then match the Falcon 9 in payload and still be at lower price. This comes from again using the first order estimate of €40 million for the two SRB's. So the Ariane 6 with no SRB's would be €35 million, as a first order estimate. So adding on two Vulcains would be €55 million, as a first order estimate. But this is still less than the $67 million price for the Falcon 9.

 In an upcoming blog post I'll discuss further the three Vulcain case showing it can match the Falcon 9 in payload. Intriguingly, by using multiple copies of such 3 Vulcain cores, I estimate 4 to 6, you can also get a 'superheavy' lift vehicle capable of 100-tons to LEO, a 'moon rocket'. Using multiple copies  of already existing cores allows you to get the 'superheavy' lift at far less development cost than the $20 billion of the SLS, or the $10 billion of the ill-conceived Superheavy/Starship.

 Manned Launchers.

 Finally, in regards to manned launchers, just use the all-liquid Ariane 6 since you no longer have the safety issues of using SRB’s on manned launchers.

 

  Robert Clark

SuperHeavy+Starship have the thermal energy of the Hiroshima bomb, Page 2: shattered windows and flying shrapnel.

 Copyright 2023 Robert Clark

 In the blog post, "SuperHeavy+Starship have the thermal energy of the Hiroshima bomb", I noted the SuperHeavy/Starship launch potentially can be damaging to people and property if it explodes. 

 I was using an exclusion radius though of only 2 miles, 3.2 km based on this hazard notice: 

 However,  this FAA report on page 22 puts the exclusion zone around the launch pad at about 5 mile radius:

https://www.faa.gov/space/stakeholder_engagement/spacex_starship/media/Draft_PEA_for_SpaceX_Starship_Super_Heavy_at_Boca_Chica.pdf

 This is about about how far away Starship launch watchers are on South Padre Island when watching the launch from outside. It’s also the distance where space launch reporters such as Tim Dodd the “Everyday Astronaut” and others report on the Starship launches from hotel rooms on South Padre Island:

SpaceX Starship: Slo-mo SN9 flight video shows explosion in stunning detail SpaceX's Starship tackled its latest "hop test" — and it didn't end well.
BY MIKE BROWN
FEB. 3, 2021. Ryan Chylinski, co-founder of Cosmic Perspective, tells Inverse he and his team were on a hotel balcony on South Padre Island during the launch — around five miles away. “We could certainly feel the rumble of the Raptors [the craft's engines] at this distance," he says. "And that explosion shockwave, wow!” he adds.
https://www.inverse.com/innovation/spacex-starship-sn9-flight

 It's also uncomfortably close to the distance to Port Isabel, TX at 6 to 7 miles away, a town of about 5 thousand people. 

 However, even 5 miles is likely to still not be a safe distance based on other large explosions at the kiloton level such as the Texas City disaster:

April 16, 1947: Ship Explosion Ignites 3-Day Rain of Fire and Death.
…It shattered all the windows in Texas City and half of those in Galveston, 10 miles away. Some debris reached an altitude of nearly 3 miles before falling back to earth. Two airplanes circling overhead were blown apart by the heavy shrapnel. A one-ton piece of the ship's propeller shaft landed 2½ miles away. Other pieces sailed 5 miles.
https://www.wired.com/2009/04/april-16-1947-ship-explosion-ignites-3-day-rain-of-fire-and-death-2/

 The Texas City explosion was at the approx. 3 kilotons of TNT level. The N-1 Soviet rocket explosion was at about the 1.2 kiloton level. Since SuperHeavy/Starship is about 2.5 times larger than N-1 we can estimate that if it were to explode it might result in an explosion at about the 3 kiloton level, comparable to the Texas City disaster.

 Then outside launch spectators on South Padre Island would be at risk of being hit by flying shrapnel even at the 5 mile distance.

Shattered Windows.

 This page gives a summary of the kinds of damage that can result in explosions at the kilotons of TNT level:

https://nuclearsecrecy.com/nukemap/?&kt=9.8&lat=25.9971256&lng=-97.1553612&hob_opt=2&hob_psi=5&hob_ft=98&casualties=1&psi=20,5,1&rem=&therm=_1st-50,_noharm-100,35&cloud=1&zm=13

 It estimates the area of shattered windows by how far away a 1 psi overpressure would reach. However, the page actually underestimates the extent of the shattered windows: while 1 psi is a nice round number to work with, even at some fraction of a psi some proportion of windows would still be shattered.

 Half the windows in the Texas City disaster for instance shattered in Galveston at 10 miles away, a distance farther away than would be predicted by the 1 psi overpressure criterion.

 Note also that large plate glass windows such as those common in store fronts, commercial buildings, and hotel rooms are easier to shatter than the small windows seen in homes. Then launch watchers in hotel rooms on South Padre Island would be at risk of being injured by shattered windows if SH/SS were to explode.

 A greater distance of shattered windows than expected also happened for example in the Soviet N-1 rocket explosion:

 The aftermath

As the shockwave and the rain of metal debris subsided, Menshikov and his colleagues all emerged out of their shelter stunned but unhurt. Flames were still raging at the launch pad to the northeast under a starry night. The power was shut off around the entire center but five minutes later most facilities started getting their lights back on. (704)

Top officials were allowed to leave their launch control bunker around 3.5 kilometers from the pad only half an hour after the explosion. When they came up to the surface, a drizzle of unburned kerosene droplets was still coming down to the ground. As was later estimated, as much as 85 percent of the propellant onboard the rocket did not detonate, reducing the force of the blast from a potential 400 tons to just 4.5 - 5 tons. (233) Also fortunately, evacuation measures proved to be effective, as all reports from various sites included "no fatalities." (685) However due to paranoid secrecy, security services apparently intentionally disconnected still operational phone lines between technical facilities and the residential area, leaving numerous family members agonizing for hours over the fate of their loved ones.

In the meantime, test officers and engineers were streaming back from their shelters to their regular work places. Menshikov and his colleagues found their fueling station in total disarray. Doors and windows were blown off, main gates crooked, equipment thrown all over the floor. Most buildings at Site 113 and surrounding facilities were in similar shape. As dawn came, they were terrified to see numerous dead birds and small animals littering the steppe.

The heaviest damage was obviously at the epicenter of the explosion. The "Right" pad of the N1 rocket at Site 110 was completely wrecked. One of the 180-meter lightning towers collapsed and was twisted into a spiral. (705) Some pieces from the rocket were found as far as 10 kilometers away and a 400-kilogram gas reservoir landed on the roof of the assembly building at Site 112, four kilometers from the pad.

Windows were blown off in buildings at Site 2, located six kilometers from the launch pad and as far as 40 kilometers away. A main display window at the Luna cafe in the main residential area at Site 10, some 35 kilometers from the epicenter, was shattered.

https://web.archive.org/web/20160410133324/http://russianspaceweb.com/n1_5l.html

  The terrible force of the explosion can be better appreciated by watching a video of it though:

The Largest Rocket Explosion Ever - The Soviet N1 Moon Rocket Failure.

 Now keep in mind the Superheavy/Starship would have 2½ times or more the force of this explosion if it did explode. 

 Then when estimating the distance to which shattered windows are to be expected a statistical evaluation must be given for the proportion of shattered windows by distance. This defense department report provides the numbers for a 50% chance of shattering:

GLASS FRAGMENT HAZARD FROM WINDOWS BROKEN BY AIRBLAST.
https://apps.dtic.mil/sti/pdfs/ADA105824.pdf

 The numbers in the report given in terms of kilopascals, kPa, where 1 kPa = 0.145 psi., show that depending on the size of the window it can shatter at overpressures down to 0.6 kPa, ~0.1 psi, well less 1 psi:

Flying Shrapnel.

 As with shattered windows the distance shrapnel can be propelled has to be given statistically rather than as single set number. This article discusses the range of distance shrapnel can travel depending on energy content of the explosion:

April 2019
COLUMNS
Engineering Case Histories: Case 106: Delayed fireball type explosions.
When a vessel containing a flammable liquid under pressure (such as those in an LNG road tanker truck) ruptures and ignites, a vapor fireball explosion can occur.

Sofronas, A., Consulting Engineer

How far away is a safe distance? Flying fragments from pressure effects may not have a reasonable safe distance. Some sources2 mention that 80% of the debris lands within 4 × Rmax and, in rare instances, up to 30 × Rmax (where Rmax is the calculated fireball’s maximum radius). 

...

Consider that an LNG tanker truck with a load of M = 19,000 kg (10,000 gal) of propane overturns, a fire erupts and the tanker explodes into a fireball after 10 min of being engulfed in a fire. The heat of combustion (Hc) for propane is 50,000 kJ/kg.

From experimental data, the fireball duration, t, can be approximately calculated as shown in Eq. 1:

t = 0.45 × (M)1/3 = 12 sec                                                                                                 (1)

At the end of the fireball growth period, t, it achieves its maximum radius (Eq. 2):

Rmax = 2.9 × (M)1/3 = 2.9 × (19,000 kg)1/3 = 77.4 m                                                   (2)

https://www.hydrocarbonprocessing.com/magazine/2019/april-2019/columns/engineering-case-histories-case-106-delayed-fireball-type-explosions

 Using the equation (2), for a 1,000,000 kg total methane fuel load for SuperHeavy/Starship, that would be a fireball radius of 290 m. Then if some proportion of the fragments can be sent 30 times the fireball radius, for SH/SS that would be 8,700 m, 8.7 km away.

 That would be for relatively small proportion of the fragments though. A statistical examination has to be done to see the proportion of the fragments that could reach say 5 km. 

 Even if the proportion of fragments that can reach beyond the 5 km exclusion zone is small, it must be kept in mind many residents and visitors in Port Isabel and South Padre Island will be outside to watch the launch, increasing the chance someone could be hit by the fragments.

 Note also, the Mexican border is inside the 5 km exclusion zone. Then Mexican citizens on the other side of the border also run the risk of being hit by flying shrapnel if there is an explosion. In such a case, SpaceX would run the risk of causing an international incident.

 Alternative Proposals.

 SpaceX does not have to launch Superheavy/Starship from the Boca Chica launch site. Note that the original proposal by SpaceX for passenger flights was from a platform 20 miles off shore because of noise levels from a launch. This can still be done. The launch tower would have to be made mobile. This is doable of course as the Saturn V, Space Shuttle, and SLS mobile launch towers showed. The Starship launch tower would have to  be carried to the coast, lifted onto a barge, then transported to a location sufficiently distant off-shore.

Another possibility would not to use a Superheavy at all. SpaceX could take a clue from the Falcon Heavy development which actually costs 1/4th to 1/6th that of entire new rocket built from scratch. SpaceX would first build a smaller two-stage with the Starship now as the first stage and a smaller mini-Starship, if you will, as the upper stage. Such a rocket could get ca. 100 tons to LEO. After many successful launches of this vehicle, Space would then proceed to a triple-core version, a la the Falcon Heavy. Such a triple-core vehicle would be able to match the 300 tons to LEO of the SuperHeavy/Starship. Note that, prior to the Falcon Heavy launch, SpaceX had launched over 1,000 Merlin engines on actual orbital flights. Such an approach would similarly result in high reliability of the Raptor engine before extending to a triple-core version. But as it is now SpaceX proposes to build the biggest rocket ever made with engines that have made zero actual flights to space.

 Note that this smaller two-stage vehicle could do both manned lunar and Mars missions in a single launch, rather  than 8 to 16 refueling flights needed for the SuperHeavy/Starship approach. When SpaceX wanted the high cargo triple-core version that then would be launched off-shore. It will almost certainly be the case the single core Starship would launch far more times than the triple-core version, just like is the case with the Falcon 9 compared to the Falcon Heavy.

 See discussion here:

The Missed Lesson of the Falcon Heavy.

https://exoscientist.blogspot.com/2023/02/the-missed-lesson-of-falcon-heavy.html

  Robert Clark

 

SuperHeavy+Starship have the thermal energy of the Hiroshima bomb. UPDATED, 3/8/2023.

Copyright 2023 Robert Clark

 I was curious what the thermal energy release would be if there is a mishap during the launch. I found this during a web search:

https://forum.nasaspaceflight.com/index.php?topic=52656.msg2189985#msg2189985

This calculated only for the Superheavy and got about 10 kilotons. When you add on also the Starship it comes to nearly that of the Hiroshima bomb at 15 kilotons.

See also the link given there of the estimate of the blast damage:

https://nuclearsecrecy.com/nukemap/?&kt=9.8&lat=25.9971256&lng=-97.1553612&hob_opt=2&hob_psi=5&hob_ft=98&casualties=1&psi=20,5,1&rem=&therm=_1st-50,_noharm-100,35&cloud=1&zm=13

 It might be argued that even if the total energy is released it won't be as bad as the blast damage from Hiroshima because it would only be slow deflagration. Unfortunately, it is now acknowledged the July, 2022 SuperHeavy fire during a fueling test was indeed a fuel-air detonation:

https://scanalyst.fourmilab.ch/t/spacex-super-heavy-explosion-beneath-booster-during-test/1676

 So the possibility of a detonation can not be ruled out. Likely, that July explosion was helped by the small volume close to the ground. But that possibility can not be ruled out during a launch. The only thing we have is the SpaceX hope it doesn’t:

“The real goal is to not blow up the launch pad. That is success.”

https://spacenews.com/shotwell-says-spacex-ready-for-starship-static-fire-test/

 Fuel-air explosions are very dangerous because the simplicity by which they can be detonated and for their power, without needing high explosives such as TNT:

 https://en.m.wikipedia.org/wiki/Thermobaric_weapon

 All that is needed is for a flammable substance to be widely and finely dispersed and for an ignition source to be present. Methane being cryogenic will flash to a gas and rapidly expand if the fuel tank is breached. Note an explosion can even happen if the liquid oxygen tank remains intact. Fuel air explosions can occur just using the surrounding air.

 It might be thought the July, 2022 explosion was just a one-off event. Unfortunately, it was not the only time a fuel-air detonation occurred during a Starship test. The explosion of the SN4 Starship in 2020 after a Raptor static test had already ended also was a fuel-air detonation. Two fuel-air detonations in their ground tests and the second one when there was not even supposed to be any ignition involved is disconcerting.

Scott Manley described the SN4 explosion here:

Scott Manley @DJSnM
Also, we know the dimensions of the structure, which means we can estimate the lateral speed of the flames, and I get 2-3 times the speed of sound in air. Suggesting the combustion was a detonation. Also note the shockwave shape rising up, supporting this being a detonation.
12:24 AM · May 30, 2020

https://twitter.com/djsnm/status/1266586181392674817

 In the SN4 explosion there was a failure of the quick disconnect valve. Either the methane was spewing out the Starship methane tank from piping at the bottom of the ship or from the quick disconnect valve from a ground methane tank. Either way it shows the extra danger when the fuel is cryogenic, unlike for kerosene: you can get flash, rapid dispersal.

 Videos of the explosion shows the methane that leaked below the ship flashing to a gas and becoming finely and widely dispersed. This is analogous to what would happen if there is a methane tank breach while in flight and if the methane has enough time to spread out before it ignites.

 Scott Manley in the video notes when the methane tank at the top of SN4 breaches, it gushes out methane at high pressure that immediately flashing into gas, resulting in an additional fireball. It doesn't appear though from this video that it detonates, merely appearing as large fire. Likely the methane here  caught fire before it became thoroughly mixed with the surrounding air to cause a fuel-air detonation. 

 By the way, on the question on whether leak came from the ships methane tank via piping at the bottom or from the quick disconnect valve from a ground methane tank, another video showed an earlier SN4 static test that completed successfully without an explosion had a methane leak at the bottom of the ship. This suggests the leak that resulted in the later explosion may have been from the ship:

STARSHIP SN4 FIXED FOR HOP, Loverro Resignation Riddle, Space Force New Mission.
https://youtu.be/sqbmLbRKzrE

 So fuel-air detonations happened twice in Starship tests by accident, with the July, 2022 SuperHeavy spin up test and the 2020 static fire test of Starship SN4. It may have also happened with the SN9 test landing crash:

SpaceX Starship: Slo-mo SN9 flight video shows explosion in stunning detail SpaceX's Starship tackled its latest "hop test" — and it didn't end well.
BY MIKE BROWN
FEB. 3, 2021
Ryan Chylinski, co-founder of Cosmic Perspective, tells Inverse he and his team were on a hotel balcony on South Padre Island during the launch — around five miles away. “We could certainly feel the rumble of the Raptors [the craft's engines] at this distance," he says. "And that explosion shockwave, wow!” he adds.
https://www.inverse.com/innovation/spacex-starship-sn9-flight

 Careful analysis of the SN9 explosion video may allow it to be determined if a fuel-air detonation did indeed occur, as Scott Manly was able to do with the SN4 explosion.

 There haven’t been all that many SuperHeavy/Starship tests where large amounts cryogenic methane fuel was released, probably less than 10. It should be a matter of concern that at least 2 and perhaps 3 fuel-air detonations occurred. It may be whenever there is large cryogenic methane release fuel-air detonations have a high probability of occurring.

 That is an additional risk of using a cryogenic fuel like methane rather than say kerosene. A cryogenic fuel will rapidly disperse as it flashes to gas unlike kerosene which will remain liquid at room temperature. Careful analysis by experts with fuel-air explosions have to be made to quantify this additional risk.

 It could be argued that a previous case of the Soviet N-1 rocket that exploded in flight resulted in a far less powerful detonation than the full energy content of the propellant: 

N1 launch explosion[edit]

Main article: N1 (rocket) § Second failure, serial 5L

On 3 July 1969, an N1 rocket in the Soviet Union exploded on the launch pad of Baikonur Cosmodrome, after a turbopump exploded in one of the engines. The entire rocket contained about 680,000 kg (680 t) of kerosene and 1,780,000 kg (1,780 t) of liquid oxygen.^[58] Using a standard energy release of 43 MJ/kg of kerosene gives about 29 TJ for the energy of the explosion (about 6.93 kt TNT equivalent). Investigators later determined that up to 85% of the fuel in the rocket did not detonate, meaning that the blast yield was likely no more than 1 kt TNT equivalent.^[59] Comparing explosions of initially unmixed fuels is difficult (being part detonation and part deflagration).

https://en.wikipedia.org/wiki/Largest_artificial_non-nuclear_explosions#N1_launch_explosion

 However, the extra danger of a cryogenic fuel like methane is that it will rapidly flash to a gas if the tank is breached, increasing the danger of a fuel-air explosion, unlike for kerosene which will remain as a liquid at room temperature. There is also an additional danger of a cryogenic fuel that I'll address later.

 A recent report is in approximate agreement with the assessment of the explosive force of the the N-1 rocket explosion:

Explosive Equivalence of Hydrocarbon Propellants. 
April 15, 2019
E. J. Tomei and James T. Nichols Launch Enterprise Engineering Launch Systems Division
https://apps.dtic.mil/sti/pdfs/AD1104981.pdf

 The primary propellants it considers are LO2/RP-1(kerosene) and LO2/ethanol. Note: it measures the explosive potential as a weight(in pounds) of TNT as a percentage of the weight(in pounds) of the propellant, rather than as a proportion of the total thermal energy possible. For example, for large amounts of LO2/RP-1, greater than 300,000 lbs, it multiplies the propellant weight times 0.30 to get the weight of TNT equivalent the explosion would have. Unfortunately, the report does not consider cryogenic methane since it did not have that among the rocket propellants that had been used for its review.

 However, the report does note there have been higher estimates found from prior testing for the propellants it does review:

2. Background 

No definitive analysis has been found defining the current explosive yield values in the Defense Explosives Safety Regulation (DESR) 6055.09 for the liquid oxygen/hydrocarbon propellant combinations, i.e., TNT equivalences of 10% for static test stands and 20%/10% for launch pads. However, per [6] these values can be traced to the 1961 Joint AF-NASA Hazards Analysis Board report. It is believed that these values resulted from extrapolating the Atlas propellant testing done by Broadview Research Corporation during 1957 and 1958. Reports can be found, however, from the 1961 period that ascribe yields ranging from 25% to 56% [24] and from 20% to 38% [52] at 250,000 lb of LO2/RP-1 propellant.

"Explosive Equivalence of Hydrocarbon Propellants", p. 10

 Using the 30% weight of TNT estimate for the N-1 rocket would give a value of 750 tons of TNT, while the current estimate is 1 kilotons (1,000 tons) or higher. This post to the NasaSpaceflight.com forum cites a U.S. intelligence report that gives it as 1.2 kilotons:

Re: Forty-five years ago today the first N-1 launch ended in an explosion

« Reply #14 on: 05/11/2014 11:04 pm »

I wish to begin by saying that the 6 kiloton figure is wholly incorrect.

I would like people to engage and do their "due diligence," and not depend on wikipedia for anything accurate.  There is historical research published about the Soviet space program, and one has to go looking for it.

I hereby provide a pathway to help answer this question under discussion in this thread about 5L.

There is indeed accurate information about this 5L explosion.  (The data comes from the NASIC boys.)

There is declassified documentation that talks to the power of the explosion of the N-1, and it is not 6 kilotons, or anywhere near it.  The NASIC report (title redacted, but issued 30 November 1971) has a table that talks to this 5L event, and it states unequivocally:  "1.2 kt explosion measured." 

Additionally, the table has measurements for:  "Explosion on Pad"; "Low Velocity Fallback"; and "High Velocity Fallback."

This table is reproduced in full in an article that appeared in the BIS (UK) periodical "Space Chronicle," appearing in the Autumn 2012 issue.  Here is the complete bibliograpihc citation:

The Ghosts of Tyuratam: Wright-Patterson, the “SL-X,” and What the US Intelligence Community Knew During the Moon Race. Space Chronicle 65 (JBIS Supplement 2): 71-90, 2012.

https://forum.nasaspaceflight.com/index.php?PHPSESSID=cf8smkflmsnmtfmj5kebkdi92h&topic=34080.msg1196912#msg1196912

 Then the 30% TNT equivalent estimate is too low by a factor of 1.6. So it should be 50% TNT equivalent for LO2/RP-1.

 The estimate it gives for LO2/ethanol of 35% TNT equivalent may also be too low by a similar amount. But taking the 35% estimate, LO2/methane has twice as much energy so we can estimate it as 70% TNT equivalent. For the 4,800 ton total propellant load of the SuperHeavy+Starship that would put it at 3.4 kilotons TNT equivalent. And if such estimates are likewise too low by a factor of 1.6 as in the LO2/RP-1 case that would put it for LO2/methane in the 112% TNT equivalent range, so to 5.4 kilotons. 

Blast Damage Beyond the Exclusion Zone.

 This then is quite concerning. Non-nuclear accidental explosions in this kiloton range caused extensive damage even kilometers away. See for example the Halifax explosion and the Texas City disaster. The damage would be even worse if it occurred in the air as in an air blast. This is how the Hiroshima bomb was designed for example in order to create the maximum extent of damage.

 The damage possible is likely to extend beyond the hazard area or exclusion zone for Starship:

 This is only an area 3 minutes, 15 seconds of latitude wide, that's 3.7 miles, 6 km. But this means the radius from the launch site is 2 miles, 3 km. Based on the Halifax and Texas City explosions the damage from such a blast is likely to extend beyond that.

Engine Failures on Starship Test Flights.

 In regards to the SuperHeavy flight, SpaceX has only done one test firing of all 33 engines together, and this was only at half power and barely more than 5 second duration. It is notable that 2 of the engines failed. Elon suggested this is ok because with 2 engines shutdown, it still has enough thrust to loft the vehicle to orbit.  But for all we know it could be that every 5 seconds or so, two additional engines could fail. We can't say one way or the other because tests of longer duration with all the engines together weren't done. 

 Because of the large number of engines, SpaceX should construct a separate engine test stand for all 33 engines together to test all the engines being able to fire for the true, full length of the booster flight, which would be minutes long, not seconds.

 In regards to those engine failures during the SuperHeavy test, it is notable that multiple times during Starship test flights it has happened that at least one engine experienced a fuel leak and exhibited a fire about the top portion of the engine, i.e., not due to the exhaust from the engine nozzle. In at least one of these cases, SN11, it resulted in explosion and complete destruction of the vehicle:

 

 So in more than one Starship test flight, 1 of the 3 engines caught fire. This raises the possibility that in case with multiple engines such as the SuperHeavy in an actual flight of several minutes length 1/3rd of the engines could catch fire or for some reason have to be shutdown. 

 In such a scenario SpaceX would be in a Catch-22 if it happened early in flight. If SpaceX shutdown that many engines, it would not have enough thrust to get positive lift, and the vehicle would come crashing down to Earth. Well then, they should initiate the Flight Termination System. The problem is the vehicle is nearly full of fuel, and exploding the vehicle could initiate a detonation of that large amount of propellant.

 In regards to that failure of SN11 being due to an engine fire, Elon Musk suggested it caused a hard start on that engine during a relight for the landing burn, which caused damage to the vehicle propellant tanks. However, another possibility comes to mind. 

 I mentioned previously that cryogenic propellants introduce another failure mode where detonation can occur: that's in the case of a BLEVE, Boiling Liquid Expanding Vapor Explosion:

https://en.wikipedia.org/wiki/Boiling_liquid_expanding_vapor_explosion

 In this case the fuel does not have to ignite. The BLEVE is due to a pressurized tank being exposed to heat which causes the tank to rupture explosively. In this case the fluid does not even have to be flammable. It can happen with steam for example. However, if the fluid is flammable it can cause additional detonations when the tank is breached.

 So an alternative explanation of  the SN11 explosion is the engine fire caused heating of the piping from the propellant tanks which led to excessive heating of the propellant and pressurization of the tanks until they ruptured.

 Scott Manly in his video on the SN11 failure was flummoxed in trying to give an explanation of the explosion and concludes it looks like it must have been some failure of the tanks in flight where they exploded from the inside:

 In the comment section to his video Manley, noted that the two haves of the methane header tank are widely separated in the debris field on the ground which supports the idea of an overpressure event:

Since recording this it’s been noticed that the two halves of the Methane header tank were separated by quite a distance, which likely meant that an over pressure event occurred inside the tank. - I.e. there might have been an explosion in the methane header tank meaning oxygen must have leaked in somewhere.

 See this image of the debris field:

 Manley, suggested oxygen may have leaked in but the over pressure just as well may have been due to overheating of the methane tank.

SpaceX ignored FAA safety warnings.

Two very, surprising and disturbing facts about the story here:

SpaceX ignored last-minute warnings from the FAA before December Starship launch.
Elon Musk’s company was told SN8’s launch would violate its FAA license, but SpaceX launched anyway.
By JOEY ROULETTE
Jun 15, 2021, 4:16 PM EDT|
https://www.theverge.com/2021/6/15/22352366/elon-musk-spacex-faa-warnings-starship-sn8-launch-violation-texas

The first surprising fact is that SpaceX ignored the FAA’s safety recommendation not to launch. This is about the SN8 flight remember that did crash and explode on landing. The FAA officials are described as being quite unhappy that SpaceX disregarded their safety recommendations:

SpaceX’s violation of its launch license was “inconsistent with a strong safety culture,” the FAA’s space division chief Wayne Monteith said in a letter to SpaceX president Gwynne Shotwell. “Although the report states that all SpaceX parties believed that such risk was sufficiently low to comply with regulatory criteria, SpaceX used analytical methods that appeared to be hastily developed to meet a launch window,” Monteith went on.

But a second fact about the article is actually alarming:

The FAA’s models showed that if the rocket exploded, its shockwave could be strengthened by various weather conditions like wind speed and endanger nearby homes. As a new launch countdown clock was ticking, SpaceX asked the FAA to waive this safety threshold at 1:42PM, but the FAA rejected the request an hour later. SpaceX paused the countdown clock.

 That’s really quite surprising that just due to weather conditions the FAA believed the Starship alone without the SuperHeavy could damage nearby homes if there were an explosion.

 This is actually alarming because with only having 3 of the earlier Raptor 1 engines, the propellant load on this test likely was 400 tons or less for it to be able to lift off with the propellant weight and dry mass weight. But this is 1/10th the propellant mass of the full Superheavy/Starship. So we can imagine for the full launch the effects could be 10 times worse if those same weather conditions obtained.

 By the way, the phenomenon of the weather extending the severity and extent of a blast wave is a known one. It's known as atmospheric focusing. It can happen when there is an inversion layer for example that reflects a shock wave back down to the ground.

  Robert Clark

The Missed Lesson of the Falcon Heavy

  Copyright 2023 Robert Clark

  Every time Gwen Shotwell or Elon Musk are interviewed about the Superheavy launch they are always fretting about a possible explosion on the launch pad, possibly damaging the launch tower.

 Shotwell and Musk have even said the test launch will be considered a success just clearing the tower without damaging it. Presumably then, the test launch will still be considered a success even if it does explode during the flight, as long as it first clears the tower. This hardly instills confidence in the reliability of the flight. Indeed it begins to look like the approach of the Russian N-1 engineers who tested the N-1 by launching it multiple times without sufficient ground testing first, resulting in the  rocket exploding on each test flight.

 One wonders, if the SuperHeavy does explode during flight, would SpaceX like the N-1 engineers before them do the next test launch again without full length test firing of all engines together, as long as the launch tower is undamaged? Suppose the launch tower is damaged, would they still take this same approach?

 What should have been done in regards to the SuperHeavy booster is to construct a separate test stand to test all 33 engines at the same time for the full, true flight burn time of the engines. The static test fire done so far was barely more than 5 seconds long, hardly a true shake out of the complete engine package at once. Plus, it was only at half thrust. During that short test, 2 engines failed. Without further information it can just as well be every 5 seconds or so another 2 engines would fail.

 Constructing a separate test stand will allow the engines all together to gradually be ramped up to full thrust and to full, true burn length duration. The automatic and manual shutoff of the two engines in the last test is encouraging. If might mean in a gradual testing program, flaws could be detected and the test curtailed if one or more engines failed. Then the flaws in those engines could be corrected and the tests conducted again.

 Note this was how it was done for the five F-1 engines of the Saturn V, conducting true, full duration tests of all five engines at once. The engines were not certified for flight until all five engines successfully completed true, full duration test firings all together, for multiple test firings.

 However, more importantly SpaceX missed major advantages of the Falcon Heavy approach of using three cores to form a heavy lift vehicle. They incorrectly concluded the Falcon Heavy was not a good approach because it cost something(!) The SpaceX engineers should have noted that for the Delta IV Heavy, also a triple-cored vehicle from existing cores, the development cost was in the range of $500 million. The correct conclusion they should have drawn is how much cheaper it was than building an entire new booster three times as big. The FH development cost also turned out about $500 million. This is only about 50% more than that of developing the original Falcon 9 at $300 million but at 3 times the payload of the current Falcon 9. 

 Actually the advantage may be even greater than that. The original Falcon 9 was only about 10 tons to LEO. So the Falcon Heavy is at 6 times the payload of the original Falcon 9. On the other hand the total development cost for all the Falcon 9 versions up to the current Falcon 9 FT has been estimated in the billion dollar range. So the Falcon Heavy increased the payload by a factor 3 over the current F9, but at a development cost less than half that of the current version.  

 Likewise to the Falcon Heavy, a triple-cored Starship could have formed a launcher at 3 times the payload of a two-stage launcher based on the Starship being the booster with a smaller mini-Starship as the second stage.This was discussed here:

Starhopper+Starship as a heavy-lift launcher. Triple-cored Starship for super-heavy lift. 2nd UPDATE, 9/2/2019: Starhopper as a lunar lander.

https://exoscientist.blogspot.com/2019/07/starhopperstarship-as-heavy-lift.html

 Quite importantly the two-stage to orbit vehicle, TSTO, would be able heavy lift 100+ tons to LEO. This is important because a 100 ton launcher is regarded as a requirement for a manned lunar mission in a single launch architecture. So already in 2021 with the Starship performing its test launches then we would already have had a manned lunar mission capable launcher. This is assuming the "Starhopper" as a small upper stage would also have had its development continued.

 This is for a single launch architecture, no 4 to 16 launches needed to refuel the Starship in orbit as a lunar lander. Note also the triple-cored version also could do a manned Mars mission in a single launch.

 And before the Falcon Heavy flew, there were over a 100 flights of the Falcon 9. That's over 1,000 actual full, operational burns of the Merlin engines. The equivalent of more than 30 full flights of the Falcon Heavy. 

  This brings up another major advantage of this approach, in regards to safety. Gwen Shotwell has said ideally Starship would have 100 launches before launching people. This is actually a logical disconnect to the Artemis missions with the Starship intending to carry people to the Moon as a lander by 2025:

Shotwell says SpaceX ready for Starship static-fire test

Jeff Foust

February 8, 2023

She said she expected Starship to fly at least 100 times before it carries people for the first time, a challenge as the company prepares a lunar lander version of Starship for NASA’s Artemis 3 mission, currently scheduled for as soon as 2025.

In her later conversation with reporters, she called that 100-flight milestone a “great goal” but suggested it was not a requirement. “I would love to do hundreds before. I think that would be a great goal and it’s quite possible that we could do that,” she said.

She noted the company has a goal of 100 Falcon launches this year. “If we can do 100 flights of Falcon this year, I’d love to be able to do 100 flights of Starship next year. I don’t think we will do 100 flights of Starship next year, but maybe 2025 we will do 100 flights.”

https://spacenews.com/shotwell-says-spacex-ready-for-starship-static-fire-test/

 But the Starship making 100 flights would mean the SuperHeavy making 100 flights by 2025. This is highly unlikely with the Superheavy not having made a single launch yet.

 Note the Falcon 9 made 85 unmanned flights before it launched crew to orbit. With, instead, a Starship  TSTO making its first flight in 2021 at over 5 times the payload as the Falcon 9, it very well could have already superseded Falcon 9 at that role and have been making ~25 flights per year over the 4 years from 2021 to 2025.

Single Stage to Orbit(SSTO) possibility.  

 The accepted interpretation of the SSTO as infeasible stems from the earliest days of the Space Age where ground launch engines only had ca. ~300 s vacuum Isp. Having to fire from the ground put severe limits on the engine efficiency as measured by Isp of engines. Because of that, it was argued an SSTO would need some major technical advance to be feasible, such as nuclear engines with ca. 900 s Isp.

 It is unfortunate that the paradigm for making a SSTO feasible was by assuming nuclear thermal propulsion. In point of fact for a kerosene-fueled engine only a ~330 s vacuum Isp was needed and for hydrogen fueled only ~440 s vacuum Isp for the ground-launch engines. Both of these became possible by the 1970's with the Russian RD-180 for kerosene-fueled at 338 s vacuum Isp and the American SSME at 452 s vacuum Isp. 

And now, with the SpaceX Raptor as a ground-launch capable engine reaching 370+ s vacuum Isp, quite significant payload becomes possible as an SSTO.

 With the Starship and mini-Starship as SSTO's radical increases in orbital flight especially for point-to-point transport would have been possible.

  Robert Clark

 

Clamshell wings for hypersonic reentry of rocket stages. UPDATED, May 4, 2023.

 Copyright 2023 Robert Clark

(Patent pending)

 It is known that large wings can reduce the speed and therefore aerodynamic heating a stage can experience during reentry. But such wings would induce high drag on ascent in addition to their high weight.

 A proposal to solve both of these issues: wings that open up from the stage sides or from the fairing for the upper stage, clamshell wings.

An overview of research on waverider design methodology

August 2017

Acta Astronautica 140

• DOI: 
• 10.1016/j.actaastro.2017.08.027

• Project: 
• Aerodynamic design theory and methodology of hypersonic waverider vehicle

• Feng Ding
• Jun Liu
• Chi-bing Shen et al. 

   The curved shape of the wings around the cylindrical rocket when opened up would provide both high lift and drags, important for the hypersonic reentry.

 For a reusable lower stage, though it would be difficult to maintain the structural integrity of the tanks for reuse when they open up to be wings, especially for maintaining a leakproof seal for the next flight. If this is to be used for a lower stage, the clamshell wings would have to be added around the stage. This would reduce the weight efficiency of the stage. However, quite likely they would still weigh quite a bit less than the propellant that has to be kept on reserve, unused, during ascent, for use for return to launch site.

 For the SuperHeavy it’s to be 7% of the propellant mass or 250 tons being kept on reserve for return to launch site. This high amount of propellant kept on reserve is a large part of the reason why the reusable versions of the Starship/SuperHeavy, just as with the Falcon 9 lose so much on reusability, 30% for partial reusability, and 50% for full reusability. 

The clamshell wings around the tanks likely can be designed to be well less than the mass of the tanks, which for the SuperHeavy is in the range of 80 tons. Wings in general commonly weigh in the range of 5% to 10% of the aircraft weight to be carried. This would be quite heavy if they had to support the fully fueled weight of the vehicle, as is normally the case with aircraft. Note though the wings would be closed around the tanks on ascent and would only open up to support the dry mass on return. Elon has estimated the dry mass of the SuperHeavy as less than 200 tons, so only at most 10 to 20 tons would be added to the stage weight, far less than the 250 tons of propellant needing to be carried now as “deadweight” during ascent. 

 For this to work you would want the clamshell wings to have high lift and drag at hypersonic speeds. The Space Shuttle for example has been described as a flying brick at hypersonic speeds having a hypersonic L/D at about 1, though its subsonic L/D was better at about 4.5. The clamshell wings will quite likely have high hypersonic L/D because of the prior research done on caret-wing hypersonic waveriders:

 The clamshell wings would be analogous in shape to the caret-shaped waveriders able to achieve high hypersonic L/D. During the return flight, we can also imagine achieving high levels of control by varying the angle on each side of the wing.

Falcon 9 opened up fairing as clam-shell wings.
Renders Credit Caspar Stanley 








Starship fairing opened up as clam-shell wings.
Renders Credit Caspar Stanley


 Note that SpaceX is returning the fairings for reuse now:




https://twitter.com/Erdayastronaut/status/1653510335582617600?s=20
 In this case though the fairings are returned, in separate halves, with the convex outer side downwards facing the airstream. We are proposing instead having the concave inner side facing the airstream. This will provide greater L/D drag ratio and also greater drag in that at high altitude hypersonic speed the clam-shell wings will be analogous to hypersonic waverider caret-shaped wings and then at low altitude, slow speed they can act as a parachute.


 This second mode is rather analogous to the Rogallo wing concept that had been proposed for capsule return from space:
High Wing Area per Weight Gives Lower Reentry Heating.


 If you can make this extra surface be lightweight then you would get low wing loading. The importance of low wing loading for reentry for spaceplanes is discussed here:


Wings in space.

by James C. McLane III
Monday, July 11, 2011
http://www.thespacereview.com/article/1880/1

At the end of the article there is this passage:

Wing loading (the vehicle’s weight divided by its wing surface area) is a prime parameter affecting flight. The antique aluminum Douglas DC-3 airliner had a big wing with a low loading of about 25 psf (pounds per square foot of wing surface). At the other end of the spectrum, the Space Shuttle orbiter has a high wing loading of about 120 psf. This loading, combined with an inefficient delta-shaped wing, makes the orbiter glide like a brick. A little Cessna 152 private plane features a wing loading of about 11 psf and modern gliders operate down around 7 psf. A space plane with huge lifting surfaces and a very low wing loading might not require any external thermal insulation at all. Building a space plane with a wing loading of, say, 10 psf should not be an impossible proposition. Perhaps some day it will be done.

{emphasis added}

Moreover, because of their curved shape they should be even more effective at slowing down the descent during reentry at high angles of attack, like a parachute.

I estimated the wing loading using this clamshell wing idea for the new Falcon 9 FT first stage, assuming they added a proportionally small amount to the weight. I used the specifications here:

Falcon 9 FT (Falcon 9 v1.2).
http://spaceflight101.com/spacerockets/falcon-9-ft

The dimensions given there are listed as 42.6 meters long and 3.66 meters in diameter, at a dry mass of 22,200 kg.

  Regarding the stage horizontally, you would have to put the swing points along the sides, rather than at the top, so that the clamshell wing on each side could open without blocking the opening of the clamshell wing on the other side. This means the wing area would be half that of the full surface area. So the surface area is (1/2)*Pi*3.66*42.6 = 244.9 m^2, 244.9*3.28^2 = 2634.86 ft^2.

The dry mass is 22,200 kg, 22,200*2.2 = 48,840 lbs. So the wing loading is 48,840/ 2634.86 = 18.5 pounds per square foot(psf). This is not 10 psf, but it is significantly better than the shuttle, and with the reduction in descent due to the curved surface this might still be enough to require minimal thermal shielding.

Also, we might be able to get additional wing area by putting clamshell wings on the upper surface, though not the same size as the lower ones so that all can open fully. This would essentially be a hypersonic biplane. It is known biplanes increase left at subsonic speeds. Recent research shows this also happens at hypersonic speeds.



The hypersonic I Plane has a unique biplane configuration to increase its payload and reduce drag. China Science Press




 For attitude control we allow the swing points to be moved up or down.

For making upper stages reusable.

 SpaceX has wanted to make the Falcon 9 upper stage reusable but has been unable to do so. This method can allow the upper stage to be reusable as well as providing a simpler approach to recovering the fairing.

 The upper stage dry mass of the Falcon 9 is about 4 tons. Then a 5% wing mass using the clamshell approach would only be an additional 200 kg, a small reduction in the payload mass. Note also the high wing area afforded by a clamshell wing approach would reduce the reentry heating as well.

 For the fairing we could allow the fairing itself to open up to form the clamshell wings. Unlike the case for the propellant tanks, you don’t have the need for the high degree precision and accuracy for closing up the wings for reuse for just the fairing.

 Another possibility might not detach the fairing at all. The fairing would be carried to orbit along with the upper stage. It would open up like a clamshell to release the payload. Then it would remain in the open position for fly back to the launch site, serving as the wings for the upper stage as well. This has the advantage of not having to recover and reintegrate the fairing and upper stage separately, but more importantly it's a simpler task than attaching variable clamshell wings to propellant tanks without damaging the structural integrity of the tanks. At a mass of the fairing at about 2 tons for the Falcon 9, this would subtract about 300 kg from the payload instead of just 200 kg for the case where the fairing was detached and clamshell wings applied to the upper stage. Actually, it would be a little better than this since the fairing being jettisoned so high in the flight, it subtracts nearly it’s weight from the payload anyway.

 Aerobraking is the proposal to slow down at Mars aerodynamically only, not using thrusters which would require carrying extra propellant at arrival. For several years hypersonic waveriders have been proposed to accomplish it:

Hypersonic waveriders for planetary atmospheres
• December 1989
• Journal of Spacecraft and Rockets -1(4)
• DOI: 
• 10.2514/3.26259
• Project: 
• Hypersonic Waveriders
• Anderson, John D., Jr
• MARK J. LEWIS
• Ajay Kothari
• Stephen Corda
•  This would be especially important if we want to reduce the travel time to Mars to limit the health effects due to high energy cosmic rays and long exposure to zero gravity, rather than the commonly proposed 6 to 8 months.
  Interestingly the SpaceX Starship upper stage if fully refueled in orbit could achieve a 12 km/s delta-v. This would be sufficient to get a small habitat for a small exploration team to Mars in 35 days.

Elon Musk

@elonmusk

·Mar 29, 2019

Replying to

@Erdayastronaut and @DiscoverMag

Probably no fairing either & just 3 Raptor Vacuum engines. Mass ratio of ~30 (1200 tons full, 40 tons empty) with Isp of 380. Then drop a few dozen modified Starlink satellites from empty engine bays with ~1600 Isp, MR 2. Spread out, see what’s there. Not impossible.

Robert Clark

@RGregoryClark

Replying to

@elonmusk @Erdayastronaut and @DiscoverMag

Holy Criminy! A 380s Isp and 30 mass ratio means over 12,000 m/s delta-v in a single stage. It could do flight to Mars in less than 35 days, IF you have orbital propellant depots and full aerocapture at Mars. See calculations here: http://exoscientist.blogspot.com/2015/08/propellant-depots-for-interplanetary.html…

3:12 AM · Mar 30, 2019

https://twitter.com/rgregoryclark/status/1111888828577574913?s=61&t=pHTwgnohxv2QCsZngqS2Iw 




Fully aerodynamic landing at Mars, aerobraking.

 Such high departure speeds would result in high arrival speeds at Mars as well, in the range of 20 km/s. I’m proposing clamshell wings emulating caret-shaped waveriders perhaps in biplane format, by approaching at low altitude, “skimming the tree-tops” so to speak, can accomplish aerobraking at Mars to land without propellant burn.
 Further modeling needs to be done to confirm this.
  Robert Clark