Author Topic: Basic Rocket Science Q & A  (Read 271212 times)

Offline kyle_baron

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Re: Basic Rocket Science Q & A
« Reply #440 on: 01/30/2010 03:16 PM »
Kyle, I'll note that scoops have their place--they make great sense for cruise missiles, which fly at one speed at one height, so the design variables are well controlled for that case. The SRB phase has the complexity of speeds ranging from 0 to Mach 4 and air pressures from sea level to 25 nautical miles, so the conditions are extremely dynamic during the period where their radiant heating is the concern.

I'm not advocating a perfect solution for the base heating problem, concerning the RS-68 engines.  I appreciate all the black and white analysis, concerning this problem.  But the final solution, is probably closer to a dark grey.  Meaning, a combination of good (not perfect) and practical solutions.  Remember, the problem is keeping the ablative nozzles from disintigratiing too quickly BEFORE the SRB's fall away.
What we do in life, echos in eternity. (Gladiator)

Offline kyle_baron

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Re: Basic Rocket Science Q & A
« Reply #441 on: 01/30/2010 03:26 PM »
I just noticed something on page 3 of the illustration of the rocket.  It's called a "Boattail shoulder".  Is this a necessary part of the boattail, or can it be ignored? 

http://www.2020vertical.com/nar_edu_cd_dev/lessons/apogee/Reports/Rocket_parts.pdf
« Last Edit: 01/30/2010 04:06 PM by kyle_baron »
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Offline Downix

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Re: Basic Rocket Science Q & A
« Reply #442 on: 02/01/2010 12:10 PM »
I just noticed something on page 3 of the illustration of the rocket.  It's called a "Boattail shoulder".  Is this a necessary part of the boattail, or can it be ignored? 

http://www.2020vertical.com/nar_edu_cd_dev/lessons/apogee/Reports/Rocket_parts.pdf
It's what holds the boattail in place.
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Offline kyle_baron

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Re: Basic Rocket Science Q & A
« Reply #443 on: 02/03/2010 03:25 PM »
I don't see how there would be any savings in money or propellent.  You still need a large (commercial) rocket to get the propellent into space.  And there aren't any on the drawing boards as far as I can tell.  Then you launch your deep space rocket with an empty EDS and "filler up" in orbit?  I see this as costing significantly more than having one large rocket.
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Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #444 on: 02/03/2010 04:54 PM »
I don't see how there would be any savings in money or propellent.  You still need a large (commercial) rocket to get the propellent into space.  And there aren't any on the drawing boards as far as I can tell.  Then you launch your deep space rocket with an empty EDS and "filler up" in orbit?  I see this as costing significantly more than having one large rocket.

Because the rocket with the empty EDS can be much smaller. and fly more often

Offline bad_astra

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Re: Basic Rocket Science Q & A
« Reply #445 on: 02/03/2010 05:00 PM »
I don't see how there would be any savings in money or propellent.  You still need a large (commercial) rocket to get the propellent into space.  And there aren't any on the drawing boards as far as I can tell.  Then you launch your deep space rocket with an empty EDS and "filler up" in orbit?  I see this as costing significantly more than having one large rocket.
Aquarius LV by Loral is designed soley for tanker duty. There's a good explanation of it on youtube somewhere.

http://homepage.mac.com/fcrossman/NorCalSAMPE/Comp_WS_papers/Turner_012204.pdf
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Offline Downix

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Re: Basic Rocket Science Q & A
« Reply #446 on: 02/03/2010 09:35 PM »
I don't see how there would be any savings in money or propellent.  You still need a large (commercial) rocket to get the propellent into space.  And there aren't any on the drawing boards as far as I can tell.  Then you launch your deep space rocket with an empty EDS and "filler up" in orbit?  I see this as costing significantly more than having one large rocket.

Because the rocket with the empty EDS can be much smaller. and fly more often
This reminds me, I've often thought that refueling an EDS might not be the most efficient method.  Could not the depot *be* the EDS fuel tank, the individual pods?  So, you fly up, dock with the fuel tank, already in orbit waiting for you.  End result, you take the fuel tank with you when you go.  The Depot then would be a central maintenance system to keep the fuel tanks cryo before usage.
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline Patchouli

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Re: Basic Rocket Science Q & A
« Reply #447 on: 02/03/2010 10:11 PM »
I don't see how there would be any savings in money or propellent.  You still need a large (commercial) rocket to get the propellent into space.  And there aren't any on the drawing boards as far as I can tell.  Then you launch your deep space rocket with an empty EDS and "filler up" in orbit?  I see this as costing significantly more than having one large rocket.

Because the rocket with the empty EDS can be much smaller. and fly more often
This reminds me, I've often thought that refueling an EDS might not be the most efficient method.  Could not the depot *be* the EDS fuel tank, the individual pods?  So, you fly up, dock with the fuel tank, already in orbit waiting for you.  End result, you take the fuel tank with you when you go.  The Depot then would be a central maintenance system to keep the fuel tanks cryo before usage.

One idea I played around with was launching the LOX and fuel tanks of the EDS separately.
Or just having a LOX depot since it is the bulk of the propellant mass.

Offline A_M_Swallow

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Re: Basic Rocket Science Q & A
« Reply #448 on: 02/03/2010 11:23 PM »
This reminds me, I've often thought that refueling an EDS might not be the most efficient method.  Could not the depot *be* the EDS fuel tank, the individual pods?  So, you fly up, dock with the fuel tank, already in orbit waiting for you.  End result, you take the fuel tank with you when you go.  The Depot then would be a central maintenance system to keep the fuel tanks cryo before usage.

The propellant needs to be taken to the depot in some sort of tank so you are a third of the way there.  The spacecraft and depot would need systems able to remove the old tanks and fit the new tanks.  The tanks would need to have some kind of docking system that the liquids can flow through.

Offline jongoff

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Re: Basic Rocket Science Q & A
« Reply #449 on: 02/04/2010 01:17 AM »
I don't see how there would be any savings in money or propellent.  You still need a large (commercial) rocket to get the propellent into space.  And there aren't any on the drawing boards as far as I can tell.  Then you launch your deep space rocket with an empty EDS and "filler up" in orbit?  I see this as costing significantly more than having one large rocket.

The key savings comes from not needing to build and pay the fixed costs an HLV (or even necessarily an "EDS") in the first place.  While having a big LOX/LH2 upper stage on the size scale of an ACES or Raptor stage would help a lot, you can actually do ESAS-class missions using existing launch vehicles if you use depots in LEO and L2.  The Centaur stages would need a Long-Duration Mission Kit (like ULA has suggested in several papers and proposals), but would otherwise be basically the same upper stage that has been flying with a good overall reliability record for decades.  So again, you save the cost of developing all that new hardware and paying all the infrastructure costs for it.  A depot, which can be a fairly simple single-launch spacecraft is likely going to be a lot less than an HLV to develop and operate.  That savings directly translates into more missions and sooner.

The other big potential savings comes down the road as the demand for lots of smaller flights provides economic incentives for the development of high flight-rate, low-cost transportation like fully-reusable LVs, gun launch schemes of various sorts, various beamed-propulsion concepts, etc.  There are methods that could drive the cost of propellant to orbit by at least an order of magnitude or more.  With a non-depot, HLV-centric architecture, even if someone invented a earth-to-LEO matter teleporter that could put propellant up for free, they wouldn't be able to benefit from it.

HLVs only win economically if you assume that a) Depots are going to be so super hard to develop, b) that they'll be super expensive to operate, c) make really pessimistic assumptions about how tanker trips are done, and d) assume that it's impossible to improve over current costs of access to orbit.

~Jon

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #450 on: 02/04/2010 11:41 AM »
HLVs only win economically if you assume that a) Depots are going to be so super hard to develop, b) that they'll be super expensive to operate, c) make really pessimistic assumptions about how tanker trips are done, and d) assume that it's impossible to improve over current costs of access to orbit.

~Jon

There is a lot more to HLV's than just economics. There are also mission requirements to consider. 5m plf's do not support a *lot* of things. Explain, for example, how depots enable large volume plf's, which will be necessary for any planetary EDL system. The *size* of the EDL system is just one example of the need for very large plf's. Only the HLV provides large plf's.

Please don't take this as being anti-depot; because I'm not. I'm very pro-depot, as you know. It's just that so many people want to occupy the polar opposites and so few take the position that a healthy program makes effective use of *both*. Stop demonizing the HLV because we need one, as the Augustine Commission clearly stated ("don't skimp on the heavy lift").

People who insist that either the depot must "win" or the HLV must "win" are either uninformed or just not being honest with themselves. As you know, the Jupiter is a HLV, but every proposal we made to Congress, NASA and industry lobbied hard, *very* hard, for the depot-based architecture. Why? Because, as I stated above, "a healthy program makes effective use of *both*".
« Last Edit: 02/04/2010 11:48 AM by clongton »
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Offline cro-magnon gramps

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Re: Basic Rocket Science Q & A
« Reply #451 on: 02/04/2010 08:59 PM »
this may have been asked before, so forgive my ignorance

can a vasimr engine be scaled up to launch a HLV (80 to 100mt)
what are the restrictions,

is there an air breathing engine (ie Skylon) that could be scaled up to HLV capabilities

is internal combustion still the most efficient method of launching a rocket of this size, and all we can do is tweek it

this is not a question of do we need a HLV, but a real question of Advanced Rocket Propulsion
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Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #452 on: 02/04/2010 09:03 PM »
People who insist that either the depot must "win" or the HLV must "win" are either uninformed or just not being honest with themselves.

Careful there. I don't think Team Direct is in a position to lecture others on honesty or truthfulness. The truth of the matter is that indeed it is not either/or if you look at it exclusively from the point of view of exploration. Depots add flexibility, but that's something you do not strictly need if you have an HLV, at least not in the early stages. On the other hand, if you look at it from the point of commercial development of space and seeking maximum synergies with exploration, then absence of an HLV is probably crucial, at least in the short term.

There's an asymmetry here: presence of depots is not crucial to exploration in the short term, but absence of HLV is crucial for commercial development of space in the short term. Presence of depots is not harmful to exploration, even in the long term and absence of HLV is not harmful to exploration, even in the long term.

That is the best argument for looking at it as either/or. Deliberately leaving out that point of view would be, well, dishonest.
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Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #453 on: 02/05/2010 12:01 PM »
People who insist that either the depot must "win" or the HLV must "win" are either uninformed or just not being honest with themselves.
Careful there. I don't think Team Direct is in a position to lecture others on honesty or truthfulness.

Are you actually accusing us of being dishonest and untruthful?
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I started my career on the Saturn-V F-1A engine

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #454 on: 02/05/2010 06:24 PM »
1) can a vasimr engine be scaled up to launch a HLV (80 to 100mt)
what are the restrictions,

2) is internal combustion still the most efficient method of launching a rocket of this size, and all we can do is tweek it

1) Power is a far bigger problem for an electric engine than thrust, so no.  You'd need gigawatts or high hundreds of megawatts.

2) Thrust is the need on a booster engine.  A reusable (and of course retrievable) air-breather is the way to go so it needs half as much tank.  I'm of the opinion that NACA was progressing nicely in building us up from the ground, and then the Moon Race got in the way.  Start where X-15 left off.  It probably ends up at rocket-based combined cycle, if one insists on a single stage.
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Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #455 on: 02/07/2010 05:35 AM »
I've always been curious about the 2 days it takes for the shuttle to reach ISS. Aside from the inspections that must be done, presumably the reason for a slow approach is to conserve fuel and thus maximize payload capacity.

Just out of curiosity, is it even possible for shuttle to reach ISS in its first orbit, even an empty shuttle?

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #456 on: 02/07/2010 10:18 AM »
I've always been curious about the 2 days it takes for the shuttle to reach ISS. Aside from the inspections that must be done, presumably the reason for a slow approach is to conserve fuel and thus maximize payload capacity.

Just out of curiosity, is it even possible for shuttle to reach ISS in its first orbit, even an empty shuttle?

No, it does have the propellant or thrust to weight ratio like Gemini.  If it did, the ISS couldn't take the plume impingement

The payload mass is not significant, the orbiter still weighs around 200k lb.

Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #457 on: 02/07/2010 04:42 PM »
I was talking about *launching* into ISS orbit. Without 50k lbs of payload, and with maximum propellant load, presumably the SSME's with OMS assist would be capable of reaching a higher orbit at liftoff. But I have no clue how much higher.

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #458 on: 02/07/2010 04:59 PM »
I was talking about *launching* into ISS orbit. Without 50k lbs of payload, and with maximum propellant load, presumably the SSME's with OMS assist would be capable of reaching a higher orbit at liftoff. But I have no clue how much higher.

The Shuttle has always been able to reach the ISS with payload.  The "slow" approach is not for saving ET propellant but OMS and RCS.  The slow approach allows for the orbiter to make small delta v changes vs the large ones that Gemini and Apollo did. 

Offline ginahoy

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Re: Basic Rocket Science Q & A
« Reply #459 on: 02/07/2010 05:14 PM »
OK. Not sure if you answered my question. What I had in mind is shuttle reaching ISS orbit at MECO. If this is possible, then it seems possible that shuttle could arrive at station vicinity within first orbit (retaining enough OMS/RCS prop for nominal docking/undocking maneuvers & landing). Just wondering if possible, not whether it's desirable.
« Last Edit: 02/07/2010 05:15 PM by ginahoy »