Wednesday, July 17, 2013

Budget Moon Flights: Ariane 5 as SLS upper stage.

Copyright 2013 Robert Clark

Delta IV Heavy Orion Circumlunar Test Flight.
I’m fairly sure looking at the capabilities of the Delta IV Heavy with the upgraded RS-68a engine, about 28 metric tons to LEO, that it could launch the Orion on that 2014 test launch on an actual circumlunar flight, not just to 3,600 miles out as currently planned. A circumlunar flight would result in a much more capable test of the Orion.

The Orion test is planned to only carry a dummy service module, so that will be much lighter. The flight is planned though to carry the launch abort system (LAS) so that detracts from the weight that can be launched.

Without the LAS the DIVH could definitely send the Orion on a circumlunar flight. With the LAS, it makes it a little more difficult to estimate since it is jettisoned before reaching orbit.

This makes the use of the SLS for that unmanned circumlunar test flight in 2017 even more dubious, since the DIVH could do that, even if removing the LAS is required. That is another reason why I argue NASA should be aiming for an actual unmanned lunar landing test with that 2017 SLS flight.

Low Cost Lunar Lander and Crew Module.
ULA has done studies on adapting the Centaur upper stage as a lunar lander stage so you would not need a huge, and hugely expensive, Altair lander. We already even have a crew module that could be used for such a lander in NASA’s SEV, which can be ready by 2017 for test flights:

Inside NASA’s New Spaceship for Asteroid Missions |
by Clara Moskowitz, Assistant Managing Editor
Date: 12 November 2012 Time: 02:30 PM ET

If the current schedule holds, NASA could test-drive a version of the SEV at the International Space Station in 2017.

Ariane 5 Core as SLS Upper Stage.
NASA is considering a version of the upper stage to be used with the Block II version of the SLS that uses RL-10 engines instead of the J-2X:

SLS prepares for PDR – Evolution eyes Dual-Use Upper Stage.
June 1, 2013 by Chris Bergin

This is expected to save on costs.

NASA also wants to encourage European participation in the proposed asteroid retrieval mission:

NASA Pitches Asteroid Capture To International Partners.
By Frank Morring, Jr.
Source: Aerospace Daily & Defense Report
June 28, 2013

Then a way to save further on development costs and to get European involvement would be to use the Ariane 5 core as the upper stage. It’s of common-bulkhead design to save mass. I recently learned it also uses the pressure-stabilized, “balloon tank”, method a la the Centaur to further save on tank mass.

The ESA also believes its Vulcain II engine can be made air-startable since this was planned for the Liberty rocket. The Vulcain uses a rather short nozzle since it is meant for ground launch, giving it a 432 s Isp. But simply giving it a nozzle extension would give it the ca. 462 s ISP of the RL-10.

Another key advantage is that because little additional development would be needed it might even be ready by the 2017 first launch of the SLS. Then this first 2017 launch of what was only to be a 70 mT interim version could have the 100+ mT capability of the later versions of the SLS. Such a version would clearly have the capability to do manned lunar lander missions.

You could also give this stage the RL-10 engines, instead of the Vulcain. The Vulcain weighs about 1,800 kg. Four RL-10′s would weigh 1,200 kg. So this would save 600 kg off the stage dry mass.

The article mentions the advantage of having different diameters for the hydrogen and oxygen tanks to maintain commonality with tooling of existing stages, and that is the reason for not having both tanks the same diameter. That would not be a problem of course with using the Ariane 5 core at a common 5.4 meter diamter. And someone noted on the Nasaspaceflight forum thread on this topic that for a uniform 8.4 m diameter, NASA could just use the same tooling for both that is used for the 8.4 meter SLS core stage tank.

For any of these possibilities it would be very good if NASA could use the composite tanks Boeing is investigating. Aerospace engineer Jon Goff on his blog noted ULA estimated their ACES proposed upgrade of the Centaur could get a 20 to 1 mass ratio by switching to aluminum-lithium for the tanks. And according to Boeing, an additional 40% can be saved off the Al-Li tank mass by using composites, resulting in an even larger mass ratio than 20 to 1:

NASA Sees Potential In Composite Cryotank.
By Frank Morring, Jr.
Source: AWIN First
July 01, 2013

Scaling up your stage mass, such as to the DUUS size, is also known to be able to improve your mass ratio. Imagine then all these mass ratio improving factors being applied. How high could the mass ratio get, perhaps to the 25 to 1, or even 30 to 1 range???

Imagine what you could do with a hydrolox stage with an ISP as high as ca. 462 s with a mass ratio as high as 30 to 1. (*)

Bob Clark

(*) By rocket equation, the delta-v is:  462*9.81ln(30) = 15,400 m/s.

Update, Sept. 28, 2013:

 Finally, NASA has acknowledged that the Block 1, first version of the SLS to launch in 2017 will have a 90+ mT payload capacity not the 70 mT always stated by NASA:

SLS Dual Use Upper Stage (DUUS).

 This is important since it means we will have the capability to do manned lunar landing missions by the 2017 first launch of the SLS:

SLS for Return to the Moon by the 50th Anniversary of Apollo 11, page 5: A 90+ metric ton first launch of the SLS.

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