Saturday, July 27, 2013

Medium lift circumlunar flights.

Copyright 2013 Robert Clark

 In the post  "Golden Spike" circumlunar flights I argued the new Falcon 9 v1.1 would be able to do manned circumlunar flights carrying a Dragon capsule. Note that this could also prove Elon's claims that the Dragon could serve as a lunar mission capsule. Moreover, such a unmanned test could be carried out this year with the first test flight of the Falcon 9 v1.1.

This is important because the original circumlunar flight carrying Apollo 8 used the huge Saturn V rocket. Then the feeling came about that even to do a manned circumlunar flight required a super heavy lift rocket such as the Saturn V. Then showing a much smaller rocket such as the Falcon 9 v1.1 could accomplish such a mission would be important to confirming the idea that lunar landing missions also could be much smaller, and much cheaper, than imagined.

 As further support of that, currently existing medium class launchers such as the Delta IV Medium and Atlas V without side boosters, can also do circumlunar missions by using a capsule half-sized to the Dragon. One such half-sized capsule would be the Orbital Sciences Cygnus, given life support systems and heat shield, as discussed in Budget Moon flights: lightweight crew capsule

 Another possibility might be the capsule designed by Andy Elson for SpaceX for the Falcon 5 rocket. Since the Falcon 5 had half the payload capability of the Falcon 9, and this capsule was to carry half the passengers of the Dragon, quite likely it would be about half-size to the Dragon:

Magic Dragon: The UK's first commercially built manned capsule demonstrator.
By Rob Coppinger on April 9, 2008 4:13 PM |

  The Delta IV Medium and Atlas V without side boosters have a payload capability of about 10 metric tons (mT) to LEO. Page 2 of Boeing's "Delta IV Technical Summary"  gives the translunar injection (TLI) payload capability of the Delta IV Medium as 3 mT, sufficient for the dry mass of the Cygnus. 

 The payload capability to TLI for the Atlas V can be estimated by Dr. John Schilling's Launch Performance Calculator by selecting the escape trajectory option. This gives about 3.4 mT capability to TLI.

 The Ariane 6 is to be a medium class launcher comparable to the Delta IV Medium and Atlas V. Then the liquid-fueled version would not only have the advantage over the solid-fueled version of being able to do manned missions to LEO but manned circumlunar missions as well.

  Bob Clark


  1. Designing to fly with much smaller rockets is exactly the right thing to do. I'm very glad you are looking so closely at this. In the 1960's, NASA had it backward, they had the Army designs for Saturn 1 and Saturn 5, and designed their flights to use those rockets, which were not originally designed for spaceflight.

    The key to overcoming launch rocket size restrictions is really nothing but LEO assembly, something we have had for a long time now. The one mission/one launch model is quite stupid, actually. It drives you toward a rocket that is one-use only, something no one else needs. That way is never cheap.

    You can build anything you want in LEO out of docked modules in the 10-to-50 ton range with rockets we already have, or will have by next year. The $/kg advantage of the bigger rocket is actually quite weak, once you get above 10 tons to LEO.

    I think your circumlunar flight with a Delta is related to a landing on the moon. One has to decide what one wants to accomplish in that landing mission. The gear and the crew to carry that mission out (whatever it is) sets the payload to be delivered to the moon's surface, and the crew size sets the ascent vehicle size. Those two together size the lander, which is a piece of the payload sent to lunar orbit.

    The travel requirements to and from lunar orbit (different payloads each way) size the vehicle that must leave LEO. If that's too big for one launch, then use orbital assembly with docked modules to match the rockets you have. What could be simpler?

    At least with a lunar mission measured in days, the men can travel in a capsule and live on the surface for more days in the lander. That's absolutely not true of a long duration mission like Mars or an NEO; that limit was established long ago in Gemini-7 as 2 weeks max in a cramped capsule.

    Similarly, if you put a longer-duration mission on the moon, you need a bigger space for them to live in. I'd suggest inflatables along the lines of what Bigelow is doing. Bigger payload to land, though. It compounds through the rocket equation to set what you assemble in LEO.

    I'd be very wary of planning to avoid that dilemma by multiple landings at the same site by multiple vehicles. There are precision guidance issues, rocket blast damage issues (mechanical and thermal), and inherent collision issues, as well as missed-landing issues. We're not technologically ready for that.

    GW Johnson

  2. I always thought the big miss in the Apollo architecture was not building the moon missions around the Saturn IB. The VAB was sized with 4 bays, so you could be processing for dual launches, and you could dock in Low earth orbit, Gemini proved you could dock a Gemini and an agena, and by building up a decent set of modules, you could make a system out of LEGO.

    putting a LEM up on a Saturn I-B in a elliptical orbit, and then docking with a CSM, would have made the whole smash way cheaper, you'd be making lots of H-1 engines, the crews would be working more efficiently, and you could invest into tooling.

    1. The Saturn 1B could only put 21 mT into LEO. It would take 7 launches to match that of the Saturn V.
      Or are you proposing a smaller architecture?

      Bob Clark

  3. Bob, What other choices are I making on Shilling's calculator. I'm not replicating your numbers.

    1. Thanks for responding. There are a lot of variations in the Atlas V. Firstly, I took the one without any side boosters since solid boosters are problematical for manned launches. This means the middle digit in the series you select should be 0.
      Then you have to select the fairing size. The 400 or 500 series determines how wide your fairing is, the 400 series being smaller.
      I assumed that the smaller 400 series fairing could be used for just the Cygnus, so that would be lower weight lost due to the fairing. Actually for carrying the Cygnus capsule we might be able to dispense with the fairing entirely, thus getting higher payload.
      Then you also have to decide to use the version of the Centaur upper stage that has 1 or 2 engines. I originally took the version with one engine because of the lighter weight. But it occurs to me that the one with two engines having greater thrust will have greater payload, so you can select that one.
      Finally for the 400 series you have to decide on the short fairing LPF or the longer fairing EPF. I took the LPF to be lighter.
      Now also when you select the "Escape trajectory" option near the bottom of the Schilling calculator, there is parameter you have to fill in called "Hyperbolic C3, km2/s2". This is indicates how far below or above you are with respect to escape velocity, where 0 would exactly be at escape velocity.
      It turns out though to do TLI since the Moon is not outside of Earth's gravity field you actually have to get a little below escape velocity. This amounts to this C3 number being -2.0 (km/s)^2. The perigee parameter inside that field I left at the default 185 km.
      At the bottom of the calculator there is another parameter that describes the trajectory. I selected "Optimal" here.
      Then when I select the Centaur with one engine which is the 401 I got the 3,400 kg value for the payload to TLI. When I select two engine option which is 402, I get 3,900.

      Bob Clark