Calling our rocket scientists! - Another dumb question

Bill White · 2004-06-25 14:16:06

This question is about rocketry basics. Please help!! :-)

http://science.ksc.nasa.gov/shuttle/tec … .html]This site reports that the Thiokol shuttle SRB weights about 1,300,000 pounds at launch with about 192,000 pounds of structural weight and 1,100,000 pounds of fuel.

This gives a mass fraction of 14.7% correct? (192/1300)

Is that enough to attain LEO if there were no payload whatsoever? Could any payload attain LEO on a lone SRB?

If yes, then $40 million divided by payload equals price per pound, correct?

What about mating a Delta or Atlas upper stage to a lone SRB and how much can be lifted to LEO?

= = =

Now is a carbon fiber SRB or a glass fiber SRB feasible?

http://www.optipoint.com/far/farbdb.htm]This site says "yes" and carbon fiber would cut structural weight by 80% while fiberglass would cut structural weight by maybe half to two-thirds.

Could such a vehicle attain LEO by itself? How much payload?

All of the structural weight savings translates directly to payload, correct?

= = =

The current steel SRB has a known and well established price. $30 - $40 million each and a 99.5+ reliability track record.

Challenger was too cold and only one failed and the post-Challenger modifications mean the current SRB is very reliable, correct? After all, how many SRBs have launched with crew at risk and not failed?

= = =

Thiokol testified to Congress as follows:

On a smaller scale – the crew exploration vehicle program plan shows demonstrator flights as early as 2008, and unmanned vehicle flights by 2011. Since this vehicle will probably only weigh 35-40K lbs, the heavy lift configuration may not be required. In keeping with the approach of maximizing use of common hardware and proven infrastructure so costs and risks can be minimized, and safety and reliability maximized, a Shuttle-derived solution should also be considered.
A human rated and flight proven CEV launch system can be available by simply utilizing a single booster combined with a liquid engine second stage. This configuration would use the same infrastructure, launch pad and people as the heavy lift transportation system. Additionally, if there is a 35-40K lb payload/cargo requirement instead of the CEV, the same system could be used – further improving overall cost effectiveness.

Does this mean a liquid stage on top of an SRB?

http://commerce.senate.gov/hearings/tes … =3362]Link

If the SRB is $40 million and the payload is 35,000 - 40,000 pounds, how much is the upper stage and final cost per pound to LEO?

GCNRevenger · 2004-06-25 16:15:28

Mmmm I would be able to give a verrry rough estimate if Astronautix wasn't down!

Probobly stick a Centaur (RL-10) based cryogenic stage on top, perhaps a new-fangled RL-60 engine.

Mad Grad Student · 2004-06-26 22:52:41

Hmm, well, it's an interesting idea, but I'm not flying on that thing! Sure, the SRBs have a perfect record when the guys launching them actually read the owner's manual, but solid rockets are inherantly vey dangerous. They can't be throttled or shut down after they're started, so if there's a problem it's a guarunteed abort, if you have one (Otherwise you go the way of Challenger ). Also, they're very inconveniant for ground crews, APCP/Aluminum rockets are incredibly toxic, and the fuel has to actually be cast into the casing. Too much static electricity and bye-bye VAB. They are not reusable, either. After each flight, the SRBs are towed to shore, dismantled, cleaned, checked-out, re-cast, reassembled, and re-mounted. You have a practically new rocket by the time you're done. Still, it would be kinda cheap and readily availible. It does seem kind of wasteful to just let all the SRB tech get thrown out. Still, I'd rather fly on whatever the next development of Spacex's Falcon rocket is. :;):

GCNRevenger · 2004-06-27 01:46:35

The idea of using the SRB as a cheap launcher was cooked up by the Thiokol people that make them if memory serves... I doubt they would be a great deal cheaper per-pound than Atlas-V when you include the upper stage and development dollars for modification, though the booster part at least would be "man rated for free." I agree entirely about the abort options issue, but if it is a question of crew survivability percentage, a super-safe rocket that fails less may be as good or better than one that fails more but is easier to escape from.

I think everybody has too much faith in Elon and SpaceX... he still hasn't launched his dinky rocket once yet, and its original advertised payload mass has shrunk substantially. His bigger Falcon-V could die of weight creep, which is bad enough already (its supposed to match the Delta-II), which would certainly rule out a reasonable manned vehicle.

Bill White · 2004-06-27 13:07:25

Why couldn't you put an escape rocket on top of the capsule like with Apollo? http://www.nasaexplores.com/show2_5_8a. … gl=58]Link

Wouldn't a CEV be on top of a 2nd stage on top of the SRB?

SRB malfunction? The escape rocket fires, pulling the CEV capsule up and away.

Add a few degrees directional control to the escape rocket and add small attitude thrusters at the top of the SRB to induce diverging trajectories for the SRB and the CEV capsule after the CEV aborts.

= = =

Compare to Atlas V - - that uses an SRB also so it beceoms bean counting.

Is the Atlas SRB segmented?

My reading suggests 6 segment Thiokol SRBs are not feasible for use on the shuttle because of stresses on the shuttle stack being beyond design limits.

Is that true for an SRB plus upper stage? How much could a six segment SRB plus RL-60 lift to LEO?

= = =

The price level for Thiokol SRBs is well established. After selling NASA 200 + of the things, knowing exactly how much they cost is not a gray area.

My reading says about $35 million each.

Besides, what else is there?

???

GCNRevenger · 2004-06-27 14:20:40

You can put an escape motor on the CEV crew capsule, but how effective it is has alot to do with the booster, considering the extreme dynamics involved.

If a large SRB like Shuttles' fails, it can explode more quickly and destroy the vehicle before the escape system could kick in with less warning. A sudden crack in the fuel cast, or a weld gives way, BOOM! No time to react... Liquid fuels may give you a little more time, an engine fire could be detected before the whole thing goes up. If only the engine goes on a liquid rocket, the rest of the vehicle could remain intact a little longer versus the SRB, where the whole vehicle would go all at the same time.

If you need to abort for some other reason, you can't shut off the engine, so you have a giant running exploding booster rocket chasing you. Trying to change the course of a giant million-pounds thrust rocket rocket with little verneer thrusters isn't going to happen, nessesitating a pretty nasty 8G+ straight-away escape.

The Atlas-V is a liquid fueled rocket with 1-5 optional mini-SRBs, which are made of graphite/epoxy like Boeing's probobly and I believe only have a single segment. It is possible that the CEV could ride on an Atlas-V with no SRBs at all, and could almost certainly ride on a "Atlas-V+" with stretched fuel tanks and no boosters. The boosters themselves are small, so if they were to fail, the results would probobly be less catastrophic than for a giant Thiokol SRB-launcher and could be ejected.

What else is there? The Atlas-V is available now, and with SRBs it would definatly be able to carry the CEV. The Delta-IV is also available, with loads of unused capacity, which could possibly carry CEV on the medium model if it is kept light enough.

Rxke · 2004-06-27 17:08:38

I think everybody has too much faith in Elon and SpaceX... he still hasn't launched his dinky rocket once yet, and its original advertised payload mass has shrunk substantially.

True.

How many launch disasters/failures can he pay before he has the wrinkles ironed out?

But about the payload? I thought it was getting *up* instead of down (4 to 6 MT to LEO)

GCNRevenger · 2004-06-27 17:13:03

Wasn't the Falcon-I supposed to deliver like 2,000lbs to LEO?

Now he's shooting for 1,400-1,500lbs, and still haven't flown once.

Bill White · 2004-06-27 19:41:33

Okay, no CEV on the Thiokol SRB.

Still, might a 5 segment SRB + liquid upper stage carry 40,000 or 50,000 pounds of uncrewed payload?

That Thiokol guy thought the 4 segment SRB + upper stage could carry 35,000 to 40,000 pounds and that should be at 1/2 the price per pound of Delta IV.

$40-$45 million for a 5 segment SRB and ?? for 2 RL-10s right?

GCNRevenger · 2004-06-27 19:58:50

The RL-10 I think goes for around $3M a pop, so I would imagine the heavy Centaur upper stage would cost in the neighborhood of $10M-12M.

Bill White · 2004-06-27 20:13:01

The RL-10 I think goes for around $3M a pop, so I would imagine the heavy Centaur upper stage would cost in the neighborhood of $10M-12M.

So that means that using the current 4 segment SRB + upper stage, the final vehicle should easily cost less than $60 million per copy after R&D is finished. Still, the SRB & RL-10 are well proven systems, right?

Now = IF = Mike Kahn is telling the truth about this configuration giving 35K - 40K to LEO (Ding that "if" bell)

THEN, we are looking at about $1500 per pound or less with a made in USA vehicle.

Pure cargo only. That 8 gee escape mode? Nah, no thanks.

Musk's Falcon V was advertised at $1,000 per pound.

GCNRevenger · 2004-06-27 20:32:38

You are talking about pounds right, careful with your units man or i'll switch back to chemistry mode and get all metric an crap.

I would put a 20-25% "advertising optimism penalty" on the cost and payload on the thing considering who's selling it, and it might be an interesting competitor to the Zenit/Proton folks, though its a little small for much else.

Nasa needs somthing fairly large, a Lunar or Mars payload of either MarsDirect or DRM-III style mission is going to weigh around 40MT. Early missions could make do with only the SDV for a launch vehicle, but for sustained flight (like to a cycler) then launching 40MT at a time would be ideal.

bolbuyk · 2004-06-28 07:33:26

They are not reusable, either. After each flight, the SRBs are towed to shore, dismantled, cleaned, checked-out, re-cast, reassembled, and re-mounted. You have a practically new rocket by the time you're done.

I think only the recovery-harcdware is reusable

As far as I know, the SRB's have a pretty low Isp, so they have serious limitations. Nobody has yet explained why an SRB is better to use over RP-1/LOx-stages (like Energia, Saturn-V).

Euler · 2004-06-28 12:28:51

The shuttle SRB's have both a low isp and a high mass ratio, even when compared with other strap-on boosters. A payloadless SRB would not be able to reach orbit; in fact, a payloadless SRB would not even be able to generate as much delta v as a Delta IV or Atlas V normally achieves with its first stage. You would need a very large, expensive, high performance upper stage to get any payload into orbit at all.

C M Edwards · 2004-06-28 13:05:59

A Centaur stage could reach orbit without a lower stage, but couldn't carry much except itself - not enough payload to make the launch worthwhile. Some other workhorse rocket stages are like that, just not the old shuttle SRB's.

Euler · 2004-06-28 14:19:52

A Centaur stage could reach orbit without a lower stage, but couldn't carry much except itself - not enough payload to make the launch worthwhile. Some other workhorse rocket stages are like that, just not the old shuttle SRB's.

Are you sure? The Centaur has a T/W ratio of less than .5, so it would have to burn more than half it's fuel before it even got off the ground.

GCNRevenger · 2004-06-28 14:27:48

The Centaur certainly could not, the RL-10 is actually quite a small engine, but has the virtue of very high Isp and reliability in a light-weight package. However, it is due to be suceeded by the RL-60 with double the thrust in a similar sized package, great for large upper stages which would ordinarily require twin RL-10 arrangements or for enhanced performance.

C M Edwards · 2004-06-28 14:45:57

Oh.

Well, if you got rid of all that pesky gravity, THEN it could get to orbit. :;):

Bill White · 2004-06-28 14:47:48

A Centaur stage could reach orbit without a lower stage, but couldn't carry much except itself - not enough payload to make the launch worthwhile. Some other workhorse rocket stages are like that, just not the old shuttle SRB's.
Are you sure? The Centaur has a T/W ratio of less than .5, so it would have to burn more than half it's fuel before it even got off the ground.

Isn't this exactly why you put it on top of an SRB or some other first stage?

The magic = if = of Thiokol's claim (it seems to me) is whether an SRB can lift a Centaur to an altitude and velocity sufficient to place a reasonable amount of payload in orbit. And can another booster do that more cheaply.

Thiokol SRBs do lift the orbiter.

The press kit claims that 2 SRBs provide 71% of the lift for the first 2 minutes.

Is it wrong to work linearly and believe that a single SRB with an upper stage of equal performance to the SSMEs could place in LEO 35% of the orbiter launch mass? (71% divided by 2)

Okay 25% of the LH2/LOX fuel gets burned during those first 2 minutes (and none of our hypothetical 2nd stage fuel gets burned while the SRB is running) so this 35% figure needs to be reduced, but by how much?

= = =

How much R&D would be needed for a 6 segment SRB?

Euler · 2004-06-28 15:53:19

I tried to calculate the payload that the SRB could orbit using a standard Centaur upper stage, and the answer I got was about 4 tons. You really want a larger, much more powerful, upper stage though. If you had a really big upper stage powered by a couple of RL-60s or an SSME, you could probably get the claimed amount of payload mass. However, the upper stage would end up being significantly more expensive than the SRB.

GCNRevenger · 2004-06-28 16:35:01

The trouble with solid rockets, is the more segments you would add, the higher the internal pressure of the engine would be, requiring thicker fuel casings to maintain safety.

So in other words, not much of an alternative to mass-producing and uprated 5M dia model with RL-60 upper stage of the Atlas-V.

BWhite · 2004-06-28 16:46:16

The trouble with solid rockets, is the more segments you would add, the higher the internal pressure of the engine would be, requiring thicker fuel casings to maintain safety.
So in other words, not much of an alternative to mass-producing and uprated 5M dia model with RL-60 upper stage of the Atlas-V.

Thanks! That makes sense :;):

GCNRevenger · 2004-06-28 23:31:32

That article floating around about upraiting the Atlas-V has piqued my curiocity... That the Atlas, simply by enlarging its fuel tanks, could loft substantialy more weight. How much could a 5-meter-diameter 1st & 2nd stage, powerd by 1x RD-180 and 1x RL-60/2x RL-10A loft?

Such a vehicle with no optional SRBs could probobly launch the CEV, getting you to orbit with only two liquid engines (very safe).

Since it would be bigger, you could add a 6th SRB engine, and then how much could it lift? Could it reach 40MT? If it could loft that much, then Earth-Orbit-Rendevous missions to the Moon would be practical, and you could even launch a MarsDirect/NASA-DRM style mission with a reasonable number of shots, if Shuttle-C/B is not available/desireable.

Or perhaps, if you only needed to launch 40MT-50MT, like for refueling a small cycler ship, or sending a payload to LEO/Moon/Mars with a cycler/tug when you don't want to do an HLLV. Both MarsDirect and DRM-III call for 40MT payloads to Mars.

This would be a viable plan if Congress outright orders Nasa to do away with ALL shuttle-related facilities and systems in favor of "private launch services only" where no large HLLV would be available.

Soyuz · 2004-06-29 15:23:59

Wasn't the Falcon-I supposed to deliver like 2,000lbs to LEO?
Now he's shooting for 1,400-1,500lbs, and still haven't flown once.

You claim this in several topics but i want to see some proof for this claim. And i recently read he's going for september 2004 (10 months late, i doubt if atlas 5 and delta 4 were launched on time).

Evidence for the opposite:

HS: By the way, someone pointed out to me that the latest figures released for the Falcon indicate 1400lbs to LEO. That's 400 more than the number that was mentioned in previous articles. Did something turn out to provide higher performance or weigh less than expected?
Musk: Our original target was at least 1000lbs to nominal reference orbit (200km, 28.5, circular), but we had a very big sandbag in there. As the actually engine and mass numbers are coming in, we are gradually reducing the sandbag. Some publications are still reporting old numbers for Falcon

http://www.hobbyspace.com/AAdmin/archiv … ]interview with Elon Musk

Article from 2002:

Slated to begin flying in 2004, the Falcon is being designed by SpaceX to launch satellites and research payloads weighing up to 1,000 pounds for less than one-third of the cost of existing launch vehicles.

http://orlando.bizjournals.com/orlando/ … tml]SpaceX to launch new rocket from Florida

Euler · 2004-06-29 16:44:35

Such a vehicle with no optional SRBs could probobly launch the CEV, getting you to orbit with only two liquid engines (very safe).

You wouldn't launch a 5 m diameter Atlas without using SRBs because the T/W ratio at launch would be less than 1.

Since it would be bigger, you could add a 6th SRB engine, and then how much could it lift? Could it reach 40MT?

It should be able to lift about 35 MT.

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#1 2004-06-25 14:16:06

Re: Calling our rocket scientists! - Another dumb question

#2 2004-06-25 16:15:28

Re: Calling our rocket scientists! - Another dumb question

#3 2004-06-26 22:52:41

Re: Calling our rocket scientists! - Another dumb question

#4 2004-06-27 01:46:35

Re: Calling our rocket scientists! - Another dumb question

#5 2004-06-27 13:07:25

Re: Calling our rocket scientists! - Another dumb question

#6 2004-06-27 14:20:40

Re: Calling our rocket scientists! - Another dumb question

#7 2004-06-27 17:08:38

Re: Calling our rocket scientists! - Another dumb question

#8 2004-06-27 17:13:03

Re: Calling our rocket scientists! - Another dumb question

#9 2004-06-27 19:41:33

Re: Calling our rocket scientists! - Another dumb question

#10 2004-06-27 19:58:50

Re: Calling our rocket scientists! - Another dumb question

#11 2004-06-27 20:13:01

Re: Calling our rocket scientists! - Another dumb question

#12 2004-06-27 20:32:38

Re: Calling our rocket scientists! - Another dumb question

#13 2004-06-28 07:33:26

Re: Calling our rocket scientists! - Another dumb question

#14 2004-06-28 12:28:51

Re: Calling our rocket scientists! - Another dumb question

#15 2004-06-28 13:05:59

Re: Calling our rocket scientists! - Another dumb question

#16 2004-06-28 14:19:52

Re: Calling our rocket scientists! - Another dumb question

#17 2004-06-28 14:27:48

Re: Calling our rocket scientists! - Another dumb question

#18 2004-06-28 14:45:57

Re: Calling our rocket scientists! - Another dumb question

#19 2004-06-28 14:47:48

Re: Calling our rocket scientists! - Another dumb question

#20 2004-06-28 15:53:19

Re: Calling our rocket scientists! - Another dumb question

#21 2004-06-28 16:35:01

Re: Calling our rocket scientists! - Another dumb question

#22 2004-06-28 16:46:16

Re: Calling our rocket scientists! - Another dumb question

#23 2004-06-28 23:31:32

Re: Calling our rocket scientists! - Another dumb question

#24 2004-06-29 15:23:59

Re: Calling our rocket scientists! - Another dumb question

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Re: Calling our rocket scientists! - Another dumb question

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