Chair Force Engineer

Monday, February 06, 2006

A CEV For All Seasons

Mark Wade's CEV rundown on Astronautix.Com is a fascinating view of the work that went into designing the CEV. However, I am put off by Mr. Wade's repeated insistence on the way he thinks the CEV should have been designed. In some ways I agree with his rants, and in others I do not. Mark Wade advocates a CEV based on the Soyuz/Shenzhou concept (orbital module + capsule + service module) and blasts the current Apollo-derived design. I feel that the Soyuz-style might be highly-efficient for earth-orbital missions, but it is optimised for neither a moon mission or a Mars adventure.

The drawback of NASA's "Apollo Redux" is the lack of applicability to Mars missions. A Mars spacecraft will be travelling much faster than a moon ship upon return to the earth. It will have to bleed off all of this extra energy in earth's atmosphere without subjecting its passengers to extreme g-forces. This means a prolonged, lifting reentry instead of the high-g, short-duration reentries of semi-ballistic capsules like Apollo. Previous studies have indicated that a biconic vehicle (like the original Kliper studies) would be best. Boeing's Earth Entry Module from their 1968 IMIS proposal is a perfect example. The Martian reentry requirement led to the design of the "Lockheed Lifting Monstrosity."

The Soyuz-style orbital module does have its advantages, such as a lighter reentry capsule. However, the orbital module goes to waste after the mission. This isn't a problem for the single-use Soyuz, but for the CEV (which will supposedly be used for as many as 10 flights in space station service,) bringing a heavier capsule back to earth can be desirable from a reusability standpoint.

Reusing the Apollo shape for the CEV also should not be viewed as a failure of design or planning. The ESAS report specifically spells out why Apollo's shape is being recycled: it's the optimal shape for generating lift at the speeds encountered by a craft returning from the moon. In fact, Buzz Aldrin predicted (among other Aldrin predictions that have come to fruition) the emergence of an enlarged "Apollo II" in his sci-fi book Encounter With Tiber.

The one area where I agree strongest with Wade is that the current CEV is too big and heavy. I would have preferred an EELV-based strategy for exploring the moon, with an all-new heavy-lifter (or an all-new reusable launcher) coming online in time to support the Mars missions. To that end, the safest option for a human launch is a single-core Delta or Atlas with no SRB's. The largest CEV that could fly on such a rocket is a 4-man CEV, as demonstrated by curmudgeonly Jeffrey Bell in his 2003 essay "Orbital Stupid Plane," which advocated such an option under the aegis of "Orbital Space Plane."

However, NASA seems set in its ways that CLV/"The Stick" will be developed (esentially from scratch) to launch the current CEV design (which has shrunk from 5.5 meters in diameter to 5 meters to make up for deficiencies in The Stick's performance.) Ultimately we have to view the CEV as NASA's own design for accomplishing its mission. The onus is now on NASA's shoulders to make their CEV design work for them, rather than second-guessing the decisions that initially drove the design. Instead of wasting our energies in criticizing these decisions, we should try to make CEV and Stick the safest and most reliable spacecraft & booster ever built. The regrets and lessons we take from CEV & Stick should be applied to future space exploration endeavours.