The Level I requirements for OSP have finally been released, after four-plus years of studies and four months of wrangling over the words. And here they are...

Requirements

1. The system, which may include multiple vehicles, shall provide rescue [medical evacuation and emergency evacuation] capability for no fewer than four ISS crew as soon as practical but no later than 2010.

Hm. Just four? I guess we aren't planning on a fully-staffed ISS, then...?

2. The system shall provide rescue capability that allows the safe return of deconditioned, ill or injured crewmembers with ongoing treatment until arrival at definitive medical care within 24 hours. Crew should not require suits in the vehicle, but the vehicle should support crew wearing suits if the situation warrants.

Now, this is a tricky one. How gentle does the ride down need to be to adequately meet this requirement? Say you have an astronaut with a spinal injury...just what sort of acceleration is that person going to be able to take? Are you going to design your entire vehicle around this requirement, providing (for example) a broad entry surface to enable a gentle reentry, at the expense of the added weight, physical complexity, and operational headaches that come with it? Any car can get you to the hospital in most emergencies, if need be -- we don't all drive ambulances.

3. The system for rescue shall provide for rapid separation from the ISS under emergency conditions followed by return to Earth.

This makes sense all around...why should it take an hour or so to depressurize, check the seals, yadda yadda, and only then separate for return? (I'm aware that there are valid safety reasons for doing so today, but this suggests to me that the current system used with Shuttle has some serious operational shortcomings.)

4. Safety requirements - system for crew rescue:

1. The availability (defined as "a full-up vehicle able to perform its mission") for the escape mission shall be at least:
   -- Objective: 99%
   -- Minimum Threshold: 95%.

2. The risk of loss of crew shall be, with high confidence, lower than the Soyuz for the rescue mission.

5. The system shall provide transportation capability for no fewer than four crew to and from the ISS as soon as practical but no later than 2012.

Oh, great...not only are we ordering a compact, we're expecting to take delivery in two years longer than it took to design, build, and fly nearly all of the hardware and infrastructure used on Apollo...from scratch. That schedule seems a bit, well, loose to me.

6. Safety requirement - system for crew transport: The risk of loss of crew shall be, with high confidence, lower than the Space Shuttle for the transport mission.

Given the risks inherent in the design of the Shuttle system, this shouldn't be too hard, after twenty-two years of experience, to accomplish. Get rid of SRBs and substitute high-temperature alloys for ceramic TPS, and you've won this battle.

7. The system shall be designed for minimum life cycle cost.

Good luck. If experience with Shuttle is any guide, those elements that cost more up-front but result in savings over the life of the program will be the first to be scrapped in the name of "cost-cutting". Plus, if an Atlas V (oh, right..."or Delta IV") is used as the expendible launch vehicle, the turnaround and maintenance costs associated with using an OSP had better be puny, else the OSP launches aren't going to be much if any cheaper than the incremental cost of launching a Shuttle.

8. The system shall meet all applicable ISS requirements for visiting and attached vehicles.

9. Compared to the Space Shuttle, the system shall require less time to prepare and execute a mission and have increased launch probability.

(Sniff) Hm...smells like apple pie. If OSP doesn't meet this requirement, it's pretty much pointless to even build it. On the other hand, it wouldn't take much at all to meet it...

10. Compared to the Space Shuttle, the system shall have increased on-orbit maneuverability.

I have this sneaking suspicion that this last item on the list was a recent addition, intended perhaps to blunt criticism that a wounded Columbia could not have reached the ISS from its orbit even had the hypothetical damage been discovered on the first orbit..."See, we've already fixed that problem with OSP!"

If the OSP, being a crew transfer and emergency return vehicle, will ONLY be operating at/from/to ISS, what is the point of all this extra on-orbit maneuverability? (Unless ISS crew rotation/rescue isn't the only end it's intended to serve...which, of course, is a whole different issue.)

Operations Concepts

1. The vehicle(s) shall initially launch on an ELV.

And the Orbiter will initially launch with an expendible tank and solid rockets. You can guarantee that if OSP ever does launch on an expendible, that will be the only vehicle ever used to launch it -- there will be no effort on NASA's part to tie up further resources in a follow-on reusable booster when they could be used somewhere more glamorous.

2. The system shall be operated through at least 2020. However, the system should be designed so that it could be operated for a longer time.

So, you're nominally planning to retire OSP, the intended successor/companion to Shuttle, five years before retiring Shuttle? After perhaps only eight years of service? Doesn't allow much time for amortization of the development and production costs, does it?

3. NASA envisions that the systems for crew rescue and crew transport could be different versions of the same vehicle design.

Sensible on the face of it. But does anyone really anticipate NASA not placing such dramatically different detailed requirements on a crew transport vehicle vs. a crew rescue vehicle that the two would be only superficially similar? The ultimate choice will be between designing two distinctly different vehicles to meet radically different and incompatible requirements, and designing one vehicle with a "compromise" (and I'm sure you know the joke there) between same.

4. The system shall provide contingency capability for cargo delivery to or from the ISS to support a minimal level of science.

I would expect OSP to have the capability to carry along some small amount of experiment consumables, small equipment, etc. on any given flight (rather than only in "contingency" situations, which implies a grounding of Shuttle and/or Progress). However, if this "capability" is defined later as the ability to deliver an ISS experiment rack, it will have a dramatic impact on the vehicle's design (since the think would probably then have to dock to station via berthing mechanism rather than the smaller docking adapter).

5. The system shall support a nominal ISS crew rotation period of 4-6 months.

I have to wonder (half seriously) if most or all of these requirements couldn't be satisfied with a reincarnated Apollo Command Module. No, really...

Posted by T.L. James on February 18, 2003 09:04 PM