Solids are better than Liquids (will be)

[ugordan]

Well, to those who say SRBs are better than liquids because they never cause a hold, the first Ares I 5-segment DM-1 static test in Utah was just scrubbed due to APU (powering the thrust vector control system) failure.

[NEOWatcher]

Well, to those who say SRBs are better than liquids because they never cause a hold, the first Ares I 5-segment DM-1 static test in Utah was just scrubbed due to APU (powering the thrust vector control system) failure.

I can understand what you are trying to say, but this was not a rocket operating as a rocket. It was just a bench test.

Is the APU even part of the booster, or is it something attached to the booster and is part of the testing equipment?

I vaguely remember similar booster tests for the shuttle being delayed and/or going horribly wrong. Can someone confirm?

[ugordan]

I can understand what you are trying to say, but this was not a rocket operating as a rocket. It was just a bench test.

Test running the same TVC hardware the shuttle flies.

Is the APU even part of the booster, or is it something attached to the booster and is part of the testing equipment?

It's part of the booster thrust vector control (TVC). Without it, there would be no controlling the shuttle stack.

I wouldn't have brought it up if it was just part of some test instrumentation.

[Antice]

Well.. I'd expect them to use used modules for a test like this so it's probably not assembled nor tested to the usual standards meant for a launch. There are many ways to screw a test up. and the most common one is human sloppiness. Why go trough all the bother when the stack ain't going nowhere right?
Or i could be wrong in that a part that exist on both solid and liquid boosters does not really say much about the reliability of either compared to the other.

Does anyone know how often APU's fail in general?

[ugordan]

Why go trough all the bother when the stack ain't going nowhere right?

Because it's an expensive test? Because you want the most representative data? Because it's packing a lot of firepower and could go really bad, not just for the booster but for the test stand as well if shoddy work is done and substandard components used?

[Antice]

Fair enough. but the stack IS bolted down securely i presume... shoddy work on that part would be most unforgivable... while i haven't been building any rockets not done any tests on such. I have been involved in testing other systems. and i know from personal experience how fast people can become lax about stuff that at first glance might not appear relevant for what is being tested.
Was the TVC supposed to actively do anything during this test?
What impact if any would a malfunctioning TVC have on the test?
Would it impact security, or is it secured hard enough to prevent anything from flying loose short of a case rupture?

[djellison]

so it's probably not assembled nor tested to the usual standards meant for a launch. There are many ways to screw a test up. and the most common one is human sloppiness. Why go trough all the bother when the stack ain't going nowhere right?

Err - not right. This is a test of hardware that is then going to become flight hardware. It has to be made, assembled, tested and verified EXACTLY like the real flight hardware, or the test is pointless.

[NEOWatcher]

Err - not right. This is a test of hardware that is then going to become flight hardware. It has to be made, assembled, tested and verified EXACTLY like the real flight hardware, or the test is pointless.

How about a link to some article with details? We can be here all day long guessing what it is they were testing.

It could be an integration test, or it could be component testing for parameter verification. (like thrust power or oscillation or fuel geometry)

Even if it were an integration test, it's still a test. It may be projected flight hardware but it is not ready flight hardware.

That's going to change the picture [of the test] quite a bit.

Does it mean a solid can fail? Sure. Does it change the overall picture? I seriously doubt it, that's why they do "loss of crew" studies.

[publiusr]

Solids are pretty reliable but when they do fail, they fail spectacularly. So much so, the Air Force has assessed that if Ares I failed early in the flight, the crew will be killed. They based this study on the failure of a Titan IV SRB back in 1998. The analysis result is that the Orion launch escape system wouldn't be able to get the crew clear of the raining debris. Nylon parachutes don't like raining debris. Here's a video of a Delta II failure caused by an solid that exploded. Such failures are rare but they do happen from time to time.

Several things can cause a large solid rocket motor to fail. Two of the more common failure causes are insulation separation and propellant cracks. Insulation separation allows the hot combustion gases to come in contact with the casing wall. This can cause more propellant to ignite prematurely. Propellant cracks cause more propellant surface area than intended to be exposed for combustion, resulting in higher pressure inside the casing. In either case, the resulting explosion is usually spectacular.

Also understand that a Delta II's solids are really not as strongly built as the SRB casings. The O-ring problem has been fixed. Ironically, the Challenger disaster showed just how rugged those solids are by surviving the ET rupture and continuing on like nothing even happened. No violent debris spewing explosion, even when the range safety officer triggered the RSS-- -this after almost flying sideways--not exactly good for 'chasing a capsule.'

A lot of this is just religion:

Solids vs liquids
pump-fed vs. pressure-fed
side mount vs top mount
winged vs ballistic
manned vs unmanned
--and so on and so forth

[Nicolas]

Well.. I'd expect them to use used modules for a test like this

Well...one of the segments flew on STS-1...Tad bit "used".

[Larry Jacks]

A lot of this is just religion:

Solids vs liquids
pump-fed vs. pressure-fed
side mount vs top mount
winged vs ballistic
manned vs unmanned
--and so on and so forth

Not quite.

Solids verses liquids has a lot of engineering basis behind the arguments. Solids are simple, mostly reliable, and relatively inexpensive. Liquids offer higher performance in the form of specific impulse.

Pressure -ed verses pump-fed also has engineering basis. A pressure fed system is simplier and less expensive, plus turbopumps are a source of failure. However, a pressure fed system has to be able to withstand tank pressures higher than the engine chamber pressure while the tanks for a turbopump system can be much lighter. Even a relatively modest rocket engine can have a chamber pressure of 300 PSI. Building tanks to withstand 300+ PSI makes for some heavy tanks. I find it interesting that SpaceX choose a pressurized tank design for the upper stage of their Falcon 1 booster. Off hand, I don't know of any other boosters with that design feature (including the Falcon 9).

Side mount verses top mount also has engineering concerns. The Shuttle C choose side mount because the engines would be in the same relative location as the Shuttle Orbiter, meaning it wouldn't need any changes to the launch pad infrastructure. It's also possible that a side mount would offer greater flexibility in payload geometry than a top mount. It's also possible that a top mount layout would offer some structural advantages - a significant engineering concern.

Winged vs ballistic - well, how many winged boosters have ever been developed? Pegasus? Any others? Perhaps there are engineering reasons why this is so, or do you simply dismiss that as "religion"?

Manned vs unmanned - each has its place in a comprohensive space program. Those who argue "either-or" on this or most other issues are setting up a false dicotomy.

[Nicolas]

versus.
I agree with the sentiment of your post. It's not "like religion" if you've got objective engineering arguments for a choice.

[publiusr]

It also depends on what you want to do. India keeps liquid fueld strap-ons to a solid first stage. Now from a structural point of view that makes sense. Yet it is actually better to have (big) solid strap-ons fall away more quickly due to their rugged, heavy design, and keep a lightweight core that is quickly staging its liquid propellant load as thrust--getting lighter all the time.

And Engineers do have their disagreements. Korolov and Glushko got hot over propellant choice--and both had good arguements.

[mugaliens]

A lot of this is just religion:

...

manned vs unmanned...

Very good response, Larry, so I'll not retread it, except to say that Ares is currently an unmanned program as it's engines, the RS-68, are not human-rated. As the RS-68 was developed for the unmanned heavy-lift Delta IV program, it will require more than 200 design changes to the RS-68 engines before they're certified to meet human-rating standards.

Earlier somone had mentioned the strength of the Shuttle's SRBs continuing to fly long (37 seconds) after the ET and Shuttle explosively disintegrated around them, and that is indeed true. Part of the reason as to why they're so sturdy is that they were designed to be reusable, unlike the external tank. One of the SRBs which flew in STS-1 has flown 48 times over thirty years! Unlike most SRBs, which have a 1% failure rate, almost always due to over-pressure causing catastrophic case failure, the SRBs are over-designed to never fail.

This video shows, rather spectacularly, what usually happens when things go wrong. Most of the explosions in the video are liquid fueled, but some are solids.

The Challenger disaster, by contrast, demonstrated that the SRBs, despite their faulty o-ring design, were made of some very tough stuff.

[ugordan]

I find it interesting that SpaceX choose a pressurized tank design for the upper stage of their Falcon 1 booster. Off hand, I don't know of any other boosters with that design feature (including the Falcon 9).

Not really that uncommon for smaller vehicles. As 2nd stages effectively operate in vacuum (you don't need high pressures for the chamber) and their tank volume is small, it simplifies an engine greatly.

BTW, Delta II second stage is also pressure-fed.

[RGClark]

Steve Cook, Ares program manager, has chosen to resign:

NASA MSFC Internal Memo: Steve Cook Resignation.
STATUS REPORT
Date Released: Thursday, August 27, 2009
Source: National Aeronautics and Space Administration
http://www.spaceref.com/news/viewsr.html?pid=32169


Bob Clark

[Glom]

Side mount verses top mount also has engineering concerns. The Shuttle C choose side mount because the engines would be in the same relative location as the Shuttle Orbiter, meaning it wouldn't need any changes to the launch pad infrastructure. It's also possible that a side mount would offer greater flexibility in payload geometry than a top mount. It's also possible that a top mount layout would offer some structural advantages - a significant engineering concern.

Would a side mount offer geometry flexibility? Unless you really wanted something to stick way out at the side, it would seem sticking it on the top would allow it to be bigger.

[ugordan]

It's also possible that a side mount would offer greater flexibility in payload geometry than a top mount.

I'm not sure that would be the case. Any payload geometry would be limited by fairing size and an inline version would win over (not)shuttle-C there, hands down. I also hear not-shuttle-C could have further limitations on payload center of gravity due to controllability issues, but this is something that would require additional analysis.

[Larry Jacks]

Regarding the potential design flexibility, I was thinking of the Energyia design. The same arrangement of large propellant tanks with RD-170 engines at the bottom and essentially 4 Zenit strap-ons meant they could switch from an unmanned payload to a Buran relatively easy. The orbital portion only had to carry the equivalent of the OMS engines to inject the payload into orbit. It was a very flexible and cleaver design.

Stacking the payload on top of the tank might prove less flexible. No matter how huge the fairing is (and it'd be very big), that will always be a design limitation when it comes to payload size. It might also be a factor with payload mass. It seems designing different sized fairings to accommodate payload differences for a side mount would be less difficult than for a top mount. That may not be true in practice, though.

[ugordan]

Note the sidemount has limits on fairing size being close to the ET and all. For example, you couldn't fit the proposed Altair lander in a sidemount. The controllability problem for bigger fairings on a sidemount arises because you're moving the center of payload cannister away from the ET and the SSMEs can gimbal out only so much. Sticking the payload on top of a vehicle poses no such problems. Controllability-wise, it's the best option as it minimizes aerodynamic drag (hence helps performance too) and lessens requirements on main engine gimbal capability. I think Direct folks at one point even suggested removing the TVC from the SRBs altogether because the inline engines would have enough control authority even without them - something not possible with shuttle-type sidemount.

[publiusr]

For example, you couldn't fit the proposed Altair lander in a sidemount. The controllability problem for bigger fairings on a sidemount arises because you're moving the center of payload cannister away from the ET and the SSMEs can gimbal out only so much. Sticking the payload on top of a vehicle poses no such problems. Controllability-wise, it's the best option as it minimizes aerodynamic drag (hence helps performance too) and lessens requirements on main engine gimbal capability.

Those are very good points.

Part of the reason as to why they're so sturdy is that they were designed to be reusable, unlike the external tank. One of the SRBs which flew in STS-1 has flown 48 times over thirty years! Unlike most SRBs, which have a 1% failure rate, almost always due to over-pressure causing catastrophic case failure, the SRBs are over-designed to never fail.

This video shows, rather spectacularly, what usually happens when things go wrong. Most of the explosions in the video are liquid fueled, but some are solids.

The Challenger disaster, by contrast, demonstrated that the SRBs, despite their faulty o-ring design, were made of some very tough stuff.

And that is all that I was getting at. The folks at Direct, by the way do use existing SRBs, as will any Ares V lite, or Magnum, etc.

What this solid vs liquid discussion is omitting is why solids are used to begin with--to augment liquids that otherwise not be able to get off the ground on their own with full propellant tanks. Saturn V had no such problems, but there have been liquids without so much thrust--and without solids to help them along, may pose a threat to their own pads.

[samkent]

Well they have eliminated the Ares test rocket hardware and software as the reason for the delayed test. It looks like the ground hardware was at fault.

I reiterate my original statement that solids do not give as many potential reasons to delay launches. Which will make them a better choice for launch vehicles.

[Larry Jacks]

Launch delays is only one criteria for judging whether solids or liquids make better boosters. The military uses solid rocket motors in missiles so reliability and rapid launch rank very high. However, when it comes to putting payload into orbit, over 50 years of booster development shows that solids are more suitable for augmenting the thrust of liquid fueled rockets. Solids are simple, reliable, and relatively inexpensive but their lower performance (primarily in terms of specific impulse) is the reason why no one has built even a medium payload space booster using only solid rocket motors. For a viable space booster, payload to orbit for a given price favors liquid fueled rockets. Launch delays, while annoying and sometimes expensive, are a lessor concern.

[ugordan]

Via NSF.com comes a presentation that's of relevance here, dates back to 2005 and it's been posted on the Augustine Commission papers page:

Crew Survival Office’s Position on the Acceptability of the Proposed Inline RSRB Launch Vehicle for Crewed Launches (ppt, 1MB) - Submitted by Leo Langston, Paul Porter, Clint Thornton, JSC Crew Survival

• In 44 years of human space flight no flight crew has been lost during ascent as the result of a totally liquid based launch vehicle
  
  - Anticipated failures and robust ascent abort system
  - Two loss of vehicle events in the manned Soyuz program ended in successful launch aborts
  
  • Soyuz 18-1 – 2nd/3rd staging separation failure
  • Soyuz T 10-1 – GSE failure; pad fire
    
• However, in 24 years of flight on SRB based systems one flight crew has been lost as the result of an SRB failure during ascent
  
  • Unexpected and unanticipated failures, and no valid abort system
  • STS 51L

“It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life. The estimates range from roughly 1 in 100 to 1 in 100,000. The higher figures come from the working engineers, and the very low figures from management. What are the causes and consequences of this lack of agreement? Since 1 part in 100,000 would imply that one could put a Shuttle up each day for 300 years expecting to lose only one, we could properly ask "What is the cause of management's fantastic faith in the machinery?"

- R. P. Feynmann, Personal observations on the reliability of the Shuttle, Report of the Presidential Commission on the Space Shuttle Challenger Accident, Appendix F

[Nicolas]

The engineers are and feel liable for the machinery they come up with. Liability makes you realistic. 1 in 100,000 is a bit, erm, gaga.

As for the other statistic: 1 and 2 aren't really the kind of values you can do loads of statistics on, but anyway. I conclude from these that the lack of a launch abort system is more of an issue than the launcher technology. Though I don't know whether a LAS would have been of much use for STS-51; were they still alive just after the ET blew up?

Not that Challenger is 100% relevant for designs without an ET, but with the limited statistics on spaceflight available, it's all we have available.

[ugordan]

As for the other statistic: 1 and 2 aren't really the kind of values you can do loads of statistics on, but anyway. I conclude from these that the lack of a launch abort system is more of an issue than the launcher technology.

Have you actually bothered to look at the document or are you simply drawing conclusions from a single snipped I extracted?

[Nicolas]

I completely read through it, thank you. I know there's lots more in the document than what I type I meant the other statistic in your post. But my point is that, looking at everything available, lack of crew escape system appears to me to be a larger issue than the launcher technology used.

My main argument for this is that the shuttle design SRB is very sturdy and does not appear to (commonly) have these immediate rupture failures for which a LAS doesn't have any time to react, removing that disadvantage compared to liquid failures. In case of STS-51 the failure still was immediate (the Et blowing up) but this is no longer relevant for the single SRB stick design.

[Larry Jacks]

Though I don't know whether a LAS would have been of much use for STS-51; were they still alive just after the ET blew up?

Yes, there is evidence the crew survived the explosion. In the wreckage, there were some manually activated air packs that were turned on. The actual acceleration forces weren't that great during the explosion, certainly not as bad as it initally appeared.

When the Challenger stack exploded, the Shuttle had a significant vertical velocity component. From memory, Challenger exploded at about 40,000 feet altitude. Estimates are that the crew compartment continued to climb to over 60,000 feet. At that altitude and with the crew compartment probably depressurized, the crew would've passed out. They were wearing little more than jump suits with a helmet. To stay alive much above 40,000 feet, you need external pressure on your body. The crew compartment impacted the ocean about 4 minutes after the explosion with an estimated deceleration of over 200 Gs. It's unlikely any of the crew were awake to see it coming and death was instant.

[ugordan]

Challenger didn't explode, it structurally broke up and the external tank breakup caused just a large deflagration with virtually no shockwave. Hollywood-style "explosion", not a real blast. To put it another way, the ET didn't destroy the orbiter, aerodynamic forces did - there goes that infamous letter q again.

[Antice]

If the leak had been detected the orbiter could have aborted. but nobody was looking for such a failure back then. apart from maybe one guy. and he wasn't being listened to.