NASA Pitches Heavy Lift Vehicle To Congress 275
BJ_Covert_Action writes "Well, Congress demanded, last year, that NASA develop a budget plan and proposal for a new heavy lift vehicle in light of the Ares V cancellation. Recently, NASA gave Congress just what they wanted. On January 11th, Douglas Cooke pitched an interim report to Congressional members detailing the basic design concepts that would go into a new heavy lift vehicle. Congress required that the new heavy lift vehicle maximize the reuse of space shuttle components as part of its budget battle with President Obama last year. As a result, NASA basically copy-pasted the Ares V design into a new report and pitched it to Congress on the 11th. The proposed vehicle will require the five segment SRB's that were proposed for the Ares V rocket. It will utilize the SSME's for it's main liquid stage. It will reuse the shuttle external tank as the primary core for the liquid booster (the same tank design that is currently giving the Discovery shuttle launch so many problems). And it will utilize the new J-2X engine that NASA has been developing for the Ares V project as an upper stage. In other words, NASA proposed to Congress exactly what Congress asked for."
Re:A Bit Left Off (Score:4, Informative)
It will reuse the shuttle external tank as the primary core for the liquid booster (the same tank design that is currently giving the Discovery shuttle launch so many problems).
fyi, not a "design issue" but a materials issue:
for Discovery's prolonged grounding, shuttle program manager John Shannon said a combination of inferior material and assembly issues is to blame. Cracks occurred in five of the 108 aluminum alloy struts in the center of the tank, which holds instruments. The damaged struts have been patched. Technicians will reinforce the remaining struts as a safety precaution, using thin 6-inch strips of aluminum. [ap.org]
Re:Let's get this straight (Score:5, Informative)
Really, it was expected that they would use the Ares V. The Augustine report had good things to say about it, their problem was with the Ares I. Killing Constellation was really about ditching that as no longer required so they could get serious about the V and the actual deep space equipment (whether it is for the moon, an asteroid, whatever). The problem that I see is that the mandate that they reuse as many shuttle components as possible means that they made some significant changes to the Ares V before giving it back to congress, namely reusing the SSMEs instead of RS-68. The SSMEs are amazingly efficient, but also amazingly expensive, so they don't fit on an expendable segment. Fortunately, they seem to have left themselves an opening to renegotiate that later, FTFProposal:
“This design would allow NASA to use existing Shuttle main engine and booster component assets in the near term, with the opportunity for upgrades and/or competition downstream for eventual upgrades in designs needed for production of engines after flying out the current inventory of main engines and booster components"
As always, though, this project is set up to fail.
“However, to be clear, neither Reference Vehicle Design currently fits the projected budget profiles nor schedule goals outlined in the Authorization Act,”
Re:A Bit Left Off (Score:4, Informative)
Re:Let's get this straight (Score:5, Informative)
Re:A Bit Left Off (Score:5, Informative)
The Shuttle SRB's in particular are built in segments which are connected by O-Rings, and that design vulnerability is part of the cause of the Challenger disaster, although this particular failing is less about SRB's in general than political ass-hattery.
Re:A Bit Left Off (Score:5, Informative)
Manufacturing solid rocket motor fuel is, essentially, a casting operation: you pour the liquid into a mold, then the liquid sets into a solid in the shape you need (and the shape is critical in rocket motors). The trouble with the solid rocket boosters as used in the Shuttle is that they are so big you have to cast them in segments, then stack them and join them. Wherever there is a seam between the segments, the burning solid fuel tends to burn into that seam; this increases the surface area that is burning, which increases pressure, which increases burn rate, which increase pressure, ad explosium. It's a very difficult (meaning: expensive and risky) problem to manage, and as we found out with Challenger, cold temperatures can cause shrinkage which opens up those seams, changing the internal geometry of the motor. Multi-segment SRBs are just plain trouble.
As anyone who has worked in large-scale casting can tell you, there are limits as to how much you can cast in a single pour. Your liquid is cooling even as you pour it, changing in volume as it cools. If you pour in multiple phases, letting it cool between phases, you're introducing seams, and subsequent pours can partially remelt previous pours, causing expansion in the previous seam and possible cracking (which are uncontrolled seams and surface area... if your solid core has internal cracking, there is a very high chance of explosion). And large continuous pours also have the potential for cracking as the early parts of the pour solidify and cure while the later parts are still molten. This, plus limits on how large a segment of solid rocket fuel you can transport without flexing (cracking) safely, is what puts upper limits on single-segment solid rocket motors.
Solid rocket motor technology on large scales comes mostly from ICBMs. You want solid motors on your ICBMs, as a single-segment motor is more rugged than a liquid fueled motor, your launch vehicle is readily transportable and self-contained, does nto need a refueling infrastructure, and is always ready to use (keeping liquid fuels in tanks for a long period of time is dangerous and high-maintenance). ICBMs don't have to throw 60,000-plus pounds of payload into orbit, therefore they don't need engines larger than can be cast in a single segment.
Nothing wrong with SRBs for sub-orbital missions with moderate payloads, or orbital missions with small payloads. But for the mass that a heavy lift booster needs to throw into orbit and beyond, they just don't scale well.
The sad fact is that the political and budgetary environment are constraints of problem-solving at NASA, just as surely as mass, temperature, volume, gravity and materials technology are constraints. Any viable proposal needs to take into account and address ALL constraints.
This is why all senior NASA people seem to get grey hair early.