Doesn’t the margin come from the second stage? The heavier the payload the longer/stronger the second stage burns.Margin margin margin. That's what a chap is saying to the Aug. Comm. right now. Ares 1 doesn't have any.
I assume you mean Soyuz. Even at its weakest, Ares is bigger, heavier, and more capable than Soyuz.I will wait and see, I will be satisfied with a performance on par with the Russians,
Here's the problem : when your staging velocity is low and upper stage initial thrust-to-weight ratio low, you suffer increased gravity losses which hurt your overall performance. This is one of the reasons the current Ares I stack pretty much hit a brick wall performance-wise.
Both EELV types actually suffer from this, but they were never designed for primarily LEO missions, but GEO missions where the low initial T/W ratio is offset by lower stage weight (one RL-10 engine only), and actually why a Falcon 9 could theoretically compete with their LEO performance even using a lower energy US. Adding a 2nd engine to the EELV US dramatically boosts their LEO performance (Atlas used to offer dual-engine Centaurs regularly and could redevelop them for A-V).
A 2nd J-2X engine is a NO-GO for Ares I because they decided so (reliability considerations - fewer engines, fewer failures, yada yada yada) and it would be overkill for the relatively light stage anyway.
basically what it boils down to is that a clean sheet design would have been better than any of the alternatives.
Funny how the term 'reliability considerations' keeps popping up with liquids.(reliability considerations - fewer engines, fewer failures, yada yada yada)
Out of the 254 SRBs used in the US manned program…
Zero launch delays due to a SRB problem.
Zero failures to ignite when commanded.
Zero in flight shut downs.
Zero SRB explosions.
On the other hand, the liquid side of the equation has caused more launch delays than I can count. Even the first launch after Columbia was delayed for two weeks due to fuel sensor problems.
basically what it boils down to is that a clean sheet design would have been better than any of the alternatives.
Sometimes, trying to save time and money by using existing hardware ends up costing far more and taking longer.
When the Ares I was first proposed, it was going to use an existing 4 segment SRB with the upper stage powered by a SSME. It was supposed to cost $14 billion to develop. Unfortunately, SSME's were designed to be started on the ground with lots of supporting equipment. It wasn't feasible to launch it in flight. So, they changed to an upgraded version of the venerable J-2 engine. However, that wasn't powerful enough so they added a 5th segment to the SRB and reportedly had to adjust other design factors. Then came serious concerns about vibration levels high enough to threaten the crew and upper stage survival, increasing Orion capsule weight and decreasing Ares I lift capacity. And the cost is now reported to be $35 billion with more delay.
There is debate as to whether a Delta IV Heavy or Atlas V variant could do the job. Personally, I believe it could. I'm also hoping SpaceX is successful with their Falcon 9/Dragon. Putting all of our eggs in a single basket leaves us vulnerable to extended downtime in the event of an accident (over 2 years each following the Challenger and Columbia accidents).
Atlas V heavy would blow both Delta IV and Ares I out of the water w/respect to LEO performance. It's very much not a paper rocket and basically ULA is waiting for someone to place an order for them to finish up the last bits of design work and deliver a flight unit 30 months later. I actually prefer it to the D-IVH, but one thing politicians apparently don't like about it is the Russian booster engine. Funny, actually, when you consider that same engine boosts a good deal of the country's top national security assets for the NRO office.
Both of them have the advantage (IMHO) of not having any solid boosters on, both are already flying (A-VH effectively, 95% hardware already flies on A-V vanilla) and have flight history. Ares I only has statistics and promises based on flight history of the shuttle booster, yet the Ares I SRB is a new development. Just like you cannot make predictions on J-2X reliability based on J-2 history, neither can 4seg and 5seg SRBs be directly comparable.
But we know powerpoint rockets are always better than real, flying hardware.
Cheaper too.But we know powerpoint rockets are always better than real, flying hardware.
As spectacular as an Atlas V Heavy would be, it might be severe overkill to carry an Orion capsule and service module to LEO. One of the other Atlas V variants might be able to do the job. This would require using solid fueled strap-ons but the industry has a lot of experience with that as opposed to using one giant solid fuel rocket for the first stage of a heavy lifter.
It wouldn't be overkill, IIRC it would have 25+ tons to LEO, a healthy margin for Orion growth during its development. You might be thinking about proposed later Phase I/II, etc incarnations, I'm talking about the Atlas equivalent of the Delta IV Heavy 3-core configuration.
The Atlas V 500 series can only lift 10 to 20 tonnes to LEO, depending on the number of solid boosters, so it's not quite enough to launch Orion. The base Atlas V HLV is expected to be able to put over 29 tonnes to LEO.
Nothing was wrong with the engine -- it shut down due to a sensor failure. A 2nd engine almost shut down, also cause by a sensor problem. At that point Challenger was beyond RTLS (return to launch site), but didn't have sufficient energy for a TAL (trans-atlantic) abort. It would have ditched in the ocean, which was non-survivable.
Fortunately after the 1st failure, redline limits were inhibited on the engines, which prevented that. However that removes all automated engine health monitoring, essentially running them in "open loop" until they blow up. So after one failure, the ability to automatically shut down the liquid engines was nullified.
While ability to shut down a liquid engine is often viewed as purely advantageous over solids, STS-51F shows this introduces the possibility of spurious shutdowns which can be potentially fatal. Also STS-51F is not the only case of a booster having spurious engine shutdowns.
Likewise on STS-93, two SSME engine controllers failed due to a short circuit, which fortunately were on two different engines. At that point only a backup controller kept each engine running. Had those failed, it would have caused a single-engine RTLS abort, which might not be survivable.
Both STS-51F and STS-93 problems could not happen with a solid propellant booster. Personally I'd rather fly on a liquid-fueled booster, but the above shows it's not that black and white.
Nothing about booster design is as simple as black and white. It's said that an airplane is a series of compromises flying in close formation. That's equally true for boosters.
In all the years of rocketry and spaceflight, no one has tried to build a substancial booster (payload more than a few thousand pounds) using only solid rocket motors. Solids have proven very good in combination with liquid fuel engines for first stages. There are sound engineering reasons why this is true. If the reports I've read are true, the Ares I design is proving the case yet again that solids aren't as suitable for being the sole power for a major first stage.
And we're back to square one again, the problems of making such an abort system work with a solid booster.
I've not even gone looking for SRB's causing delays. This was just there this morning. Thought I'd put it out there. You're being dishonest claiming that SRB's never cause delays.Originally Posted by Spaceflightnow.com story
Oh - and we've had TWO inflight shutdowns of SRB's. Just after the Challenger explosion - remember - the one caused by an SRB.
Last edited by djellison; 2009-Aug-02 at 06:58 PM.
Any chance of replacing the Ares I solids with the old Saturn F-1 engines?
This Astronautix page gives the F-1 a vacuum thrust of 1,740,134 lbf at a weight of only 18,498 lb for a thrust to weight ratio of nearly 100 to 1.
The Astronautix page on the Ares I solids give it vacuum thrust of 3,480,122 lbf but an empty weight of 221,230 lb (!) for a thrust to weight ratio of only 16 to 1 (!)
The tank mass for a kerosene-LOX engine is only about 1/100th that of the propellant mass. So even if you used the same propellant mass as the Ares I solids of about 1,400,000 lb that would only add 14,000 lb to the lower stage empty mass. But actually the propellant mass would probably be less since the F-1 had a better Isp at 304 s compared to 265 s for the Ares I solids.
Given this, how much larger payload could we launch to LEO using the 2 F-1 engines in place of the Ares I solids as the 1st stage?
How much could we launch to LEO using just 1 F-1 engine as the 1st stage?
More on the subject in this article.
It is a "no brainer" to conclude that if there is an inhibitor failure (the cause of the Titan IV A accident used in the model) that there will be little chance of escape. In fact, that sort of failure will happen too quickly to be detected and effective abort action to be taken.
However, that hardly precludes a successful abort and escape triggered by the detection of other failure modes.
If you think you are going to escape with high probability from any sort of explosive failure mode, whether involving liquid or solid rocket motors, you are kidding yourself. These things typically happen really fast. I have seen quite a few and the reaction time is at best a couple of milliseconds. When you watch high speed films, all of the action takes place in 1-2 frames even at rates of 1000 frames/sec.
The other item that applies is that even in an explosion like the one in the study, the propellant debris is not uniformly distribute, so nothing is "enveloped". Yes, there can be a lot of chunks of burning propellant in the air. But they are also spread out, and do not "envelop" in the sense of a cloud of hot gas. It is closer to a shotgun pattern with a very open choke. So, a parachuting capsule might encounter disaster from a large chunk of burning propellant, or it might get away relatively unscathed. In either case it is less vulnerable that it would be if it were still attached to the ruptured rocket motor case. The hard part would be to get far enough away prior to the actual case rupture so as to survive the shock waves in the first place.
The analysis presented appears to come from branches of the Air Force that do not regularly deal with solid rockets.
The point of the study was that high aerodynamic loads imparted by Ares I prevent Orion and its LAS from getting far enough away even in this case when there are a few seconds of warning time.
Maybe so, but Air Force is still responsible for that big red button and USAF probably don't like the prospect that destroying a SRB after an abort would fry the crew alive. Death from firendly fire. RSO is responsible for public safety, but a proposition like this would present a moral dilemma to him.The analysis presented appears to come from branches of the Air Force that do not regularly deal with solid rockets.
BTW that analysis may well have had the failure mode that you describe, but there then another failure within a few years prior (1993?) that did result from an inhibitor problem relating to a poor repair procedure. Sorry, if I got my failures mixed up -- faulty memory.
I appreciate the work of range safety. They have a tough job. But they have that same tough job and moral delimma right now with the STS. The only thing missing is the escape mechanism.Originally Posted by ugordon
I have strong personal doubts that any launch abort system will work effectively. Rocket failures just don't often give much notice. But I am also convinced that such a system will do no harm, and might work in some situations.
I have enough experience to be quite confident that a prediction of certain failure is no more credible than a prediction of certain success.
* need to destroy SRB early so it doesn't chase you (doesn't feel that max-Q as much as small capsule), a rough model by a member on another forum suggested aborted Ares I stack would pass by the Orion ~5 seconds after abort
* need to wait as long as possible so you clear the SRB debris field afterwards
Yep, and that one was also a Titan IV.BTW that analysis may well have had the failure mode that you describe, but there then another failure within a few years prior (1993?) that did result from an inhibitor problem relating to a poor repair procedure. Sorry, if I got my failures mixed up -- faulty memory.
If the dynamic pressure completely countereacts the thrust from the LAS then you are hosed. But if not one ought to be able to get away by applying thrust transverse to the trajectory, to escape laterally. You would then have to wait for the solids to pass by before deploying the parachute, but that would seem to be a good strategy in any case. 5 seconds strikes me as a long time for this to happen, particularly under max Q conditions.
In the life of a solid rocket failure 5 seconds is usually indistinguishable from 2 weeks. Which simply supports the notion that the escape and abort is not going to handle most SRB failure modes, but might handle other types of failures.
But only might. In reality we have zero experience with any sort of in-flight safe abort of a space launch. Rockets are, because of high performance requirements (gravity is a bear) inherently a set of single-point failure modes. Riding rockets is inherently dangerous. You do everything possible to assure success, but these things are not Greyhound busses.
The LAS is at least as much public relations as it is rocket science. But it is better than nothing.
Last edited by DrRocket; 2009-Aug-02 at 09:41 PM.
any escape system that has been thought trough applies transverse forces to escape the vehicle. just like the catapult seat in a jet fighter that rights itself up to avoid smashing the pilot into the ground during a low altitude inverted ejection.
The LES does not have to outpace the first stage for more than half a second or so. once the capsule is gone on it's way, the rocket is no longer an aerodynamic vehicle and what happens with it is anybody's guess.
Delaying the self destruct by 5 seconds wont affect range safety by much at that altitude. Even if you apply range violation immediate destruct options, that is just a chance one has to take. range violation may or may not happen depending on the chain of events that lead to the abort scenario.
Like I mentioned in another thread: What if they detonate just the joints of the segments? That would stop any additional forward thrust and keep the propellant contained.
someone claimed internal pressure would rip the segments apart if you did that.
I cant see why that would happen actually since the segments themselves arent being ripped apart when the pressure is at max during normal operation.
popping the segments from the bottom and up by starting with dumping the throat of the rocket would relieve the pressure a great deal by itself.
Probably a better way would be to sever the SRB nozzle first, let the pressure inside drop and then just rip the casing apart, any old way. The problem is it's not so simple to drop the nozzle without risking it jamming the throat and blowing everything up again. IIRC the way the nozzle is nested inside the SRM makes this difficult.