Bleg: EELV Loft Trajectory Abort Loads
Hey guys, I'm working up a short blog entry about the whole "abort loads due to the lofted trajectories used by the EELVs" issue, and was wondering if anyone here actually has any idea how high the loads really are. Worst case I imagine would be a ballistic reentry from about ~240km (which is the peak altitude that the EELVs reach during their initial ascent). I know someone with a simulator that could likely get me a rough estimate on the numbers, but I was wondering if anyone actually knows the numbers NASA supposedly came up with--because I sure as heck couldn't find them anywhere. The ESAS report said that it exceeded the limits found in NASA STD 3000, Section 5, but if you look in there, it's very unclear which numbers they picked. One number for reentry was as low as 4Gs, but others were much higher.
I guess the thing that bugs me is that without including numbers, it's really hard to evaluate how serious of a problem that was with the EELVs. Without numbers it isn't engineering--it's handwaiving.
I guess the thing that bugs me is that without including numbers, it's really hard to evaluate how serious of a problem that was with the EELVs. Without numbers it isn't engineering--it's handwaiving.
posted by Jon Goff at 12:05 AM
14 Comments:
The CAIB Report, Ch. 10, makes reference to “Reentry Survivability Analysis of Delta IV Launch Vehicle Upper Stage,” JSC-29775, June 2002. This may be part of what you're looking for, but I haven't found a copy on the web, not even on the NASA Technical Report Server. (Hmmm...) Perhaps we're not supposed to see that report...
Just as a follow-on, a Senate hearing on 05/18/05 includes the following summary in its contents:
"VII. Launching Humans on Atlas V and Delta IV Boosters
The possibility of using the current Atlas V and Delta IV rockets to launch a new, piloted spacecraft has led the Astronaut Office to look closely at the crew safety implications of this option.
• According to the OSP–ELV Human Flight Safety Certification Study Team Report, the Atlas V and Delta IV rockets do not meet many of the NASA safety standards specified or referenced in NPG 8705, the Human Rating Requirements. Major changes needed to bring the vehicles into compliance would include at least: adding failure tolerance for critical systems, redesigning for greater structural safety factors (human-rated spacecraft use 1.4; Atlas V and Delta IV rockets use 1.25), adding fault detection and isolation functions, making the range destruct philosophy compatible with maximum crew survivability, wiring for insight and intervention by the crew and ground control, performing the detailed risk analyses needed for human rating, supplementing process controls in all phases of production, and flight testing to human rating standards.
• The Atlas V and Delta IV boosters were built to be cost-effective for their manufacturers, insurers, and customers, considering the value of the non-human payloads they were designed to carry. Although cost-effectiveness includes reliability considerations, safety is not the prime driver for satellite launches. The expense of human rating these existing rockets by adding design margins, redundancy, instrumentation, process control, command capability, and testing, might make them uneconomical for their original mission and could potentially
be as costly as building a new human-rated booster.
• The reliability of Atlas V and Delta IV rockets is not precisely known because they are too new. Given insufficient flight data, one method for predicting reliability
is to assume that a new system is about as reliable as a similar, existing system. The OSP–ELV Human Flight Safety Certification Study Team used the flight record of Atlas, Delta, and Titan rockets developed under U.S. Government contracts and launched since 1990 to predict the reliability of the Atlas
V and Delta IV. These rockets have been launched 236 times and reached safe orbits 230 times. The resulting reliability estimate is 0.950 or better with 95 percent confidence. The boosters’ potentially low reliability would place excessive burden on abort mechanisms to save the crew. The abort or escape system
would need a reliability near 0.980 for the complete launch system to meet the Astronaut Office crew survivability target. Proposed abort and escape systems were judged to be incapable of rescuing the crew from stack detonations occurring with little or no warning. These failures occur often enough to prevent even a high-reliability abort or escape system from meeting its safety requirement.
• Atlas V and Delta IV boosters fly to orbit on highly lofted trajectories because of second-stage performance limitations and range destruct line-of-sight requirements.
If a piloted spacecraft had to abort near the apex of such a trajectory, it would hit the atmosphere at a high speed and a steep angle. The resulting heat and acceleration loads on the crew compartment would be severe and possibly not survivable.
In summary, the Atlas V and Delta IV rockets should be measured against a set of concrete, specific, verifiable requirements for carrying humans before being selected for that purpose. A safer launch option might be identified by objectively comparing the advantages and drawbacks of a range of existing, modified, and new launch systems relative to those requirements."
So it appears that some of the assumptions built into the current criticisms derive from a study done on the EELV suitability as a launch vehicle for the OSP.
Given the design differences between a lifting-body like OSP and a blunt capsule like CEV seems to be destined to be, then I wonder if the results are really applicable. Could it be that NASA is using it as a fig-leaf because they really want to do the proposed ESAS architecture and haven't really done their homework on whether the same assumptions still hold true?
The Kistler K-1 flies a lofted trajectory to ensure that its first stage (the Launch Assist Platform) can fly back to the launch site. It was just selected for COTS.
There will be a Paper presented at an upcoming Conference that dispels the misinformation about EELV Human Rating Compliance. You must recall the EELVs were baselined for OSP. It was determined at that time that EELVs could be Human Rated.
I've read from some EELV advocates that Lockheed and Boeing eventually solved most of the problems with OSP. Besides, you can put multiple RL-10:s in.
This is a weird issue. I've also read from some that ESAS didn't look at the EELV options well enough.
Atlas 552 (2 RL10's) would be fine
Jon, I just ran Orbiter with a nonlifting ballistic entry. From 250 km, with various horizontal velocities, I got:
V0 Amax
m/s m/s2
0000 89
1000 95
2000 112
3000 145
4000 154
5000 165
6000 165
7000 139
I doubt if the 0.25 L/D of an Apollo-like capsule would make much difference for these except the last case, which comes in pretty shallow. Worst case was under 20 gees, though.
-Doug Jones
Doug,
Thanks for running the simulator. I think you'd be surprised how much of a difference even a .25 L/D can make for fractional orbital reentry G's. At least that's what Dave's seen from some of the various number crunching excercises he's done--once you have horizontal velocity, lift can really cut down on the G's. It might be worth rerunning the numbers. 16G's is a bit hot. What kind of duration were you seeing?
Thanks!
~Jon
The Conference Paper will address Human Rating the existing Atlas V. You can get information on evolved Atlas at the following Website: http://www.lockheedmartin.com/wms/findPage.do?dsp=fec&ci=17607&rsbci=14917&fti=0&ti=0&sc=400
Anonymous,
There will be a Paper presented at an upcoming Conference that dispels the misinformation about EELV Human Rating Compliance. You must recall the EELVs were baselined for OSP. It was determined at that time that EELVs could be Human Rated.
That'd be interesting to read. If you could send me a copy to my gmail address jongoff at gmail dot com, I'd be interested in blogging a bit about it.
~Jon
I will certainly send it to you wen it becomes available!
Doug, you must be thinking of the Gemini capsule, which has a L/D of .25. The Apollo has an L/D of .6.
Jon,
You can find the paper at the Lockhhed Martin website:
http://www.lockheedmartin.com/wms/findPage.do?dsp=fec&ci=17607&rsbci=14917&fti=0&ti=0&sc=400
Scroll down to the document entitled "Atlas V for Commercial Passenger Transportation". This Paper is being presented at Space 2006.
NASA STD 3000 imposes a 4G limit but this in reality was for the return of an injured crewman from orbit (and was arbitrary even for this). It was not intended to apply to launch abort,
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