Specific impulse of liquid methane for rocket balloon

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Prelates, Moderators General

Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Tue Sep 17, 2013 5:14 pm UTC

Anybody have any idea what the specific impulse of liquid methane is? Supposedly it's slightly higher than kerosene, but is far denser and a good deal warmer than liquid hydrogen.

Also, any clue how one would estimate the energy required to turn STP methane into a liquid?

Methane is lighter than air, so you could conceivably use it to rise into the upper atmosphere, then burn a portion of it to provide energy to liquify the rest. Then you've got your liquid rocket fuel sitting in the upper atmosphere ready to go; you need only to have brought some LOX and a rocket engine, and you're set for orbit.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Tue Sep 17, 2013 6:03 pm UTC

Sorry double post.
Last edited by Tass on Tue Sep 17, 2013 6:09 pm UTC, edited 1 time in total.
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Tue Sep 17, 2013 6:08 pm UTC

davidstarlingm wrote:Anybody have any idea what the specific impulse of liquid methane is? Supposedly it's slightly higher than kerosene, but is far denser and a good deal warmer than liquid hydrogen.


SpaceX aims for 380s with Raptor.


davidstarlingm wrote:Methane is lighter than air, so you could conceivably use it to rise into the upper atmosphere, then burn a portion of it to provide energy to liquify the rest. Then you've got your liquid rocket fuel sitting in the upper atmosphere ready to go; you need only to have brought some LOX and a rocket engine, and you're set for orbit.


There is no way in hell that would reduce the price to orbit. Way to complex and expensive.

If you really needed the launch assist, why not just lift the ready rocket with a balloon? Or better a plane, which also gains you a bit of speed. Why put the liwuifying plant up there? What does it gain?
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby speising » Tue Sep 17, 2013 6:16 pm UTC

i think it was already repeatedly pointed out in this forum that the expensive part of rocketry is not the first 10km of height, but getting the things up to orbital speed. avoiding a bit of dense atmosphere would be nice, but not worth the enormous additional effort.
speising
 
Posts: 1098
Joined: Mon Sep 03, 2012 4:54 pm UTC
Location: wien

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Tue Sep 17, 2013 6:38 pm UTC

Tass wrote:
davidstarlingm wrote:Methane is lighter than air, so you could conceivably use it to rise into the upper atmosphere, then burn a portion of it to provide energy to liquify the rest. Then you've got your liquid rocket fuel sitting in the upper atmosphere ready to go; you need only to have brought some LOX and a rocket engine, and you're set for orbit.

There is no way in hell that would reduce the price to orbit. Way to complex and expensive.

Not so expensive. Methane is cheap; compressors are lightweight.

If you really needed the launch assist, why not just lift the ready rocket with a balloon?

Because you lose the balloon, and because you have to carry the fuel, which means you have to have a bigger balloon anyway.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Tue Sep 17, 2013 6:59 pm UTC

davidstarlingm wrote:
Tass wrote:
davidstarlingm wrote:Methane is lighter than air, so you could conceivably use it to rise into the upper atmosphere, then burn a portion of it to provide energy to liquify the rest. Then you've got your liquid rocket fuel sitting in the upper atmosphere ready to go; you need only to have brought some LOX and a rocket engine, and you're set for orbit.

There is no way in hell that would reduce the price to orbit. Way to complex and expensive.

Not so expensive. Methane is cheap; compressors are lightweight.

If you really needed the launch assist, why not just lift the ready rocket with a balloon?

Because you lose the balloon, and because you have to carry the fuel, which means you have to have a bigger balloon anyway.


Yes. Methane is cheap. In fact so cheap that it would be around 0.1% of the price of launching the rocket. You don't care one bit whether you waste a bit of it.

It is the high tech rocket that costs.

The complexity of the operation increases dramatically. The rocket needs to be designed for this. You couldn't just strap an existing launcher under the balloon. We are talking a billion dollar development program. Designing it to be fueled at 10kms height is a constraint that will drive the price up. The only thing to compensate for this is the slightly increased payload due to the higher start; but, as has been pointed out, the potential energy of ten kilometers is next to nothing compared to orbital energy.

The one thing that makes launching at altitude worth thinking about is actually not the height, but the reduced pressure, making it possible to improve Isp by using a nozzle better suited for vacuum.
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Tue Sep 17, 2013 7:05 pm UTC

Tass wrote:The one thing that makes launching at altitude worth thinking about is actually not the height, but the reduced pressure, making it possible to improve Isp by using a nozzle better suited for vacuum.

Right, I couldn't give a damn about the height. It's the lower atmospheric pressure that we're craving here. Low drag, better Isp. As we figured out in another thread, atmospheric drag eats up 30-40% of the work done by the Space Shuttle main engines and booster rockets. That's significant.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Tue Sep 17, 2013 7:14 pm UTC

davidstarlingm wrote:
Tass wrote:The one thing that makes launching at altitude worth thinking about is actually not the height, but the reduced pressure, making it possible to improve Isp by using a nozzle better suited for vacuum.

Right, I couldn't give a damn about the height. It's the lower atmospheric pressure that we're craving here. Low drag, better Isp. As we figured out in another thread, atmospheric drag eats up 30-40% of the work done by the Space Shuttle main engines and booster rockets. That's significant.


Okay, so again: If you want to develop a rocket for air launch, why not just lift it with a blimp or zeppelin, or even a throw-away balloon. Why over-complicate things by attempting to fabricate cryogenic fuel out of your lifting gas at altitude?
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Tue Sep 17, 2013 7:21 pm UTC

Tass wrote:If you want to develop a rocket for air launch, why not just lift it with a blimp or zeppelin, or even a throw-away balloon. Why over-complicate things by attempting to fabricate cryogenic fuel out of your lifting gas at altitude?

Just to see if it could be done in a SSTO design.

Burning methane to compress methane could have other uses, too. If we ever did have anything approximating a floating city, I imagine that self-fueled compression would be one of the most energy-efficient ways possible of creating vertical ferries.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Tue Sep 17, 2013 7:40 pm UTC

davidstarlingm wrote:
Tass wrote:If you want to develop a rocket for air launch, why not just lift it with a blimp or zeppelin, or even a throw-away balloon. Why over-complicate things by attempting to fabricate cryogenic fuel out of your lifting gas at altitude?

Just to see if it could be done in a SSTO design.

Burning methane to compress methane could have other uses, too. If we ever did have anything approximating a floating city, I imagine that self-fueled compression would be one of the most energy-efficient ways possible of creating vertical ferries.


SSTO?! Balloon launch assist would add to the margins of a TSTO, maybe even so much that it could be worth it. Smart people have toyed with the idea at least. STSO from the balloon (1.5 stages), no way, the assist is too weak. I mean, you could do it technically, but you'd have hardly any payload, and you could not make it reusable, so whats the point?

And you want to take the compressor and balloon with you?!? Now you have completely wiped out the payload.

SSTO is only worthwhile if you have the margins to make it reusable and still have payload. Skylon might make it work, by having hardware that is pretty damn optimized for rocket flight, while still being able to bring it to mach 5.5 at 30km with very little use of mass.

Rocket engineers fret over getting a little bit of extra power to weight in the turbopumps that pump the propellant into the engines. You want to bring bring the entire machinery to liquefy the whole tank. Compressors might be light weight (state-of-the-art largely driven by rocket engineering) but they are not that lightweight. By the way, were would you dump all the heat from the heat of condensation and from thermodynamic inefficiencies?
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Tue Sep 17, 2013 9:25 pm UTC

Tass wrote:SSTO?! Balloon launch assist would add to the margins of a TSTO, maybe even so much that it could be worth it. Smart people have toyed with the idea at least. STSO from the balloon (1.5 stages), no way, the assist is too weak. I mean, you could do it technically, but you'd have hardly any payload, and you could not make it reusable, so whats the point?

Reusability was actually a major thrust (no pun intended). We talk about a single stage to orbit vehicle, but what we really want is single craft to orbit. A totally reusable one. Because that's what's really cool. "Hey, let me hop in my spaceplane and take you for a couple of orbits, darling." "Oh, sunrise in space is SO romantic!"

The idea would be a delta-wing spaceplane containing a hybrid jet/rocket engine with a nozzle optimized for low-pressure flight. Fill one set of tanks with LOX; fill collapsible sky bag with methane at STP, hop in.

The methane takes you to altitude, where you convert it to liquid methane. Use a heat exchanger to put the waste heat to creative use, like auxiliary power or something. Pump the liquid methane into your jet engine for as long as you can, then shut off your jet intake and go straight to full liquid rocket operation as you boost into orbit. So there's only one fuel source needed besides oxidizer.

Probably belongs more in fictional science, sure.

But the concept of burning your lifting gas to compress your lifting gas is still interesting (and, as far as I can tell, novel).
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Copper Bezel » Wed Sep 18, 2013 4:09 am UTC

Wait a second. This seemed workable, or nearly so, for a glider, but a spaceplane is a very different sort of vehicle. The profile needs high velocity to generate net aerodynamic lift, but the jet engine can't come on until the blimp is fully retracted. That means that during the entire process of liquifying the methane, you have neither aerostatic nor aerodynamic lift.

I think you will not go to space today.
~ I know I shouldn't use tildes for decoration, but they always make me feel at home. ~
User avatar
Copper Bezel
 
Posts: 793
Joined: Wed Oct 12, 2011 6:35 am UTC
Location: Mission, Kansas, USA

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Wed Sep 18, 2013 6:14 am UTC

davidstarlingm wrote:Use a heat exchanger to put the waste heat to creative use, like auxiliary power or something.


That's thermodynamically impossible. Well sure, if you have a cold sink available then you can get some work out of a heat source, but in the end you have to shed entropy. The lower temperature you get your waste heat too, the harder it is to get rid of.

This takes lots of time and/or mass.

And of course theres the point of dropping like a stone while this goes on, which I didn't bother bringing up last night.
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Wed Sep 18, 2013 1:54 pm UTC

Copper Bezel wrote:Wait a second. This seemed workable, or nearly so, for a glider, but a spaceplane is a very different sort of vehicle. The profile needs high velocity to generate net aerodynamic lift, but the jet engine can't come on until the blimp is fully retracted. That means that during the entire process of liquifying the methane, you have neither aerostatic nor aerodynamic lift.

I think you will not go to space today.

Yeah, that's problematic. However, aerostatic lift decreases gradually, and you can start your engines slightly before the blimp is retracted, and there's a glide ratio to think about as well.

Tass wrote:
davidstarlingm wrote:Use a heat exchanger to put the waste heat to creative use, like auxiliary power or something.

That's thermodynamically impossible. Well sure, if you have a cold sink available then you can get some work out of a heat source, but in the end you have to shed entropy.

A cold sink like the entire atmosphere?

And of course theres the point of dropping like a stone while this goes on, which I didn't bother bringing up last night.

Clearly a problem for engineering.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Copper Bezel » Wed Sep 18, 2013 2:14 pm UTC

Aerostatic lift decreases linearly with the volume you draw out, but - and i realize this is a tautology - buoyancy is going to be net-negative for the entire time between hitting peak altitude and complete retraction of the balloon, over which time your downward acceleration goes from zero to one g. And the balloon is going to be a drag chute the moment you turn the engines on, because it can't have any kind of rigid internal structure and has to fit into a tiny space.

And this is many, many times bigger than your glider's balloon would need to be. Like, in playing with the other topic, I'd found that an empty 747 is something like 65 times denser than air. Your space plane is going to be hitched underneath a collapsing, deformable balloon many, many times its own volume, and already basically free-falling but for the parachute effect itself.

I don't see what kind of glide ratio you can have with a space plane with a drag chute, either. It's not likely to have much in the way of wing area. It's designed for exactly the opposite kind of flying.
~ I know I shouldn't use tildes for decoration, but they always make me feel at home. ~
User avatar
Copper Bezel
 
Posts: 793
Joined: Wed Oct 12, 2011 6:35 am UTC
Location: Mission, Kansas, USA

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Wed Sep 18, 2013 3:29 pm UTC

Copper Bezel wrote:I don't see what kind of glide ratio you can have with a space plane with a drag chute, either. It's not likely to have much in the way of wing area. It's designed for exactly the opposite kind of flying.

Yeah, it really seems that way.

Oh well.

Still interested in the non-spacelaunch version.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Wed Sep 18, 2013 7:05 pm UTC

davidstarlingm wrote:
Tass wrote:
davidstarlingm wrote:Use a heat exchanger to put the waste heat to creative use, like auxiliary power or something.

That's thermodynamically impossible. Well sure, if you have a cold sink available then you can get some work out of a heat source, but in the end you have to shed entropy.

A cold sink like the entire atmosphere?


Yes, obviously. And as I discussed in the part you cut out in order to liquefy this much methane quickly, you need a damn good thermal coupling to that atmosphere. That takes a lot of mass.

My point was: Making work out of the waste heat makes it harder to shed the remainder, not easier.
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby Copper Bezel » Wed Sep 18, 2013 9:06 pm UTC

davidstarlingm wrote:
Copper Bezel wrote:I don't see what kind of glide ratio you can have with a space plane with a drag chute, either. It's not likely to have much in the way of wing area. It's designed for exactly the opposite kind of flying.

Yeah, it really seems that way.

Oh well.

Still interested in the non-spacelaunch version.

Yeah, me too. The numbers don't seem as absurdly unfavorable there, the aerodynamics of the glider are better suited for the purpose, and more of the potential energy lost in the fall gets turned into some moderate lateral momentum that the glider has more use for. The blimp will still be larger than the glider, and I worry about the weight of the skin; as a lower limit, lifting a typical 8 m sailplane, with the plane empty, ignoring the weight of the blimp itself, and using hydrogen, would take something like an 18 m spherical balloon, and about twice that volume with methane.
~ I know I shouldn't use tildes for decoration, but they always make me feel at home. ~
User avatar
Copper Bezel
 
Posts: 793
Joined: Wed Oct 12, 2011 6:35 am UTC
Location: Mission, Kansas, USA

Re: Specific impulse of liquid methane for rocket balloon

Postby cjameshuff » Sat Sep 21, 2013 4:59 pm UTC

davidstarlingm wrote:Right, I couldn't give a damn about the height. It's the lower atmospheric pressure that we're craving here. Low drag, better Isp. As we figured out in another thread, atmospheric drag eats up 30-40% of the work done by the Space Shuttle main engines and booster rockets. That's significant.


I don't know what you came up with in that other thread, but atmospheric drag losses are in the area of 100-150 m/s, so more like 1%. Reduction in gravity losses due to the altitude are almost certainly more significant, but you've still got a lot of climbing to do before you can start approaching orbital velocity.

Reducing atmospheric density reduces drag, but it also reduces buoyant lift in the same proportion. The higher the launch altitude, the larger the balloon, and you're going to need to start moving while the balloon's largely inflated. I don't see this reducing drag losses overall. Also, methane's the lower mass part of the fuel, with 2 O2 molecules per CH4 molecule, given a stoichiometric mix (likely fuel-rich in reality, but this is close). If you tank up all your methane at altitude, that only saves you from lifting 20% of your propellant mass to that altitude.

This also means your rocket's total mass is still nearly what it is on the ground...something around 80%, plus the mass of the balloon, compressors, heat exchangers, air-breathing engines, etc. Assume rocket + balloon is in the area of 300 tonnes (comparable to the Falcon 9, Atlas V, or Delta IV). At an altitude where the atmospheric density is 1/4 what it is at sea level, a spherical balloon will need to be 170 m across...91000 m^2 of material to deflate and fold up mid-launch and carry to orbit and back for your SSTO idea. That's about double the size of the Red Bull Stratos balloon, and you're only matching the small single-core versions of these launchers. (Oh, and that's 460 tonnes of methane to lift the vehicle, of which you need ~60 tonnes, the remainder being burned to liquefy those 60 tonnes and stay aloft as the balloon is deflated. The cost isn't much, but it's still rather gratuitously inefficient given your goal of increasing efficiency.)

And you've still got an orbital rocket with tanks, engines, etc. Modestly increasing the size of the propellant tanks and using somewhat higher-thrust engines or extra engines gets you to the same altitude from the ground, plus a good deal of upward velocity, with a lot less added operational complexity than an airborne launch platform. Air launch really doesn't make sense. (Yes, the Pegasus exists...it's also the highest cost way to put mass in orbit that's actually in operation.)

Also, look at operations. Rockets can launch in the rain or snow, in moderate wind, etc. They can be grounded by adverse conditions, but aren't enormously sensitive (apart from launch systems like the Shuttle which were a pain anyway). Can you see your balloon launching in this? A hundred-meter-scale balloon launch carrying an orbital rocket needs near-perfect ground conditions and favorable high-altitude conditions...you can't have it drifting back over populated areas as it climbs to launch altitude.

Next, you can't do test fires under actual launch conditions. SpaceX just had to delay a launch because of issues they found in a test fire, and they did another test fire a couple days later that confirmed they fixed the problem. You can't do this if you're dangling your vehicle from a balloon, especially if you're fueling it from that same balloon's lift gas. You similarly can't abort a launch and try again later, you're committed when the balloon leaves the ground. And you've added a lot more machinery for failures to happen in.
User avatar
cjameshuff
 
Posts: 84
Joined: Fri Oct 29, 2010 11:24 pm UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Mon Sep 23, 2013 8:20 pm UTC

cjameshuff wrote:I don't know what you came up with in that other thread, but atmospheric drag losses are in the area of 100-150 m/s, so more like 1%. Reduction in gravity losses due to the altitude are almost certainly more significant, but you've still got a lot of climbing to do before you can start approaching orbital velocity.

In the other thread, we painstakingly tracked down actual telemetry data from the Space Shuttle launches along with the thrust profiles of the SSMEs and the SRBs and calculated the exact amount of work done by the engines. Another forum-goer estimated the total energy contained in the SRBs and SSME tanks and ran the same basic equations from the other direction. In the end, we came to the same result: at least a third of the work done by the engines is lost to atmospheric drag.

If you tank up all your methane at altitude, that only saves you from lifting 20% of your propellant mass to that altitude.

Hmm, very good point. I suppose we could use a denser oxidizer, but that would probably cost us more in specific impulse than it's worth. Yet another reason why the spacelaunch version probably isn't as good of an idea as non-orbital variety.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby cjameshuff » Tue Sep 24, 2013 12:54 am UTC

davidstarlingm wrote:In the other thread, we painstakingly tracked down actual telemetry data from the Space Shuttle launches along with the thrust profiles of the SSMEs and the SRBs and calculated the exact amount of work done by the engines. Another forum-goer estimated the total energy contained in the SRBs and SSME tanks and ran the same basic equations from the other direction. In the end, we came to the same result: at least a third of the work done by the engines is lost to atmospheric drag.


Well, one of you must have misplaced a decimal point, because you're about an order of magnitude high. Gravity losses are roughly in that area and are sometimes called gravity drag, but that's a quite different thing from aerodynamic drag. Look at page 5 here for a comparison of the various losses...just the Shuttle's steering losses were about 3x its drag losses:
https://engineering.purdue.edu/AAE/Acad ... _19_27.pdf


davidstarlingm wrote:
If you tank up all your methane at altitude, that only saves you from lifting 20% of your propellant mass to that altitude.

Hmm, very good point. I suppose we could use a denser oxidizer, but that would probably cost us more in specific impulse than it's worth. Yet another reason why the spacelaunch version probably isn't as good of an idea as non-orbital variety.


What oxidizer do you see as doing better in this respect than O2? You need over twice the mass of fluorine to fully oxidize methane, most other oxidizers are just carriers of oxygen. (There's a reason LOX is so widely used...)
User avatar
cjameshuff
 
Posts: 84
Joined: Fri Oct 29, 2010 11:24 pm UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby Tass » Tue Sep 24, 2013 7:40 am UTC

I think part of the problem might be that one of you thinks in terms of energy, the other in delta-v.

When it comes to rockets delta-v is the relevant term.
User avatar
Tass
 
Posts: 1887
Joined: Tue Nov 11, 2008 2:21 pm UTC
Location: Niels Bohr Institute, Copenhagen.

Re: Specific impulse of liquid methane for rocket balloon

Postby cjameshuff » Tue Sep 24, 2013 11:42 am UTC

Tass wrote:I think part of the problem might be that one of you thinks in terms of energy, the other in delta-v.


I thought of that, but don't see a way to turn 107 m/s into 1/3 the energy.

Another thought was that at max Q, aerodynamic drag might eat up 1/3 of the thrust of the engines, especially since the main engines throttle down to 70% to avoid excessive stresses on the vehicle, but this only occurs over a brief portion of the overall flight. My best guess is that either a decimal point got misplaced or gravity losses (which tend to be about 10 times higher than drag losses) were lumped in.
User avatar
cjameshuff
 
Posts: 84
Joined: Fri Oct 29, 2010 11:24 pm UTC

Re: Specific impulse of liquid methane for rocket balloon

Postby davidstarlingm » Tue Sep 24, 2013 1:46 pm UTC

cjameshuff wrote:
Tass wrote:I think part of the problem might be that one of you thinks in terms of energy, the other in delta-v.


I thought of that, but don't see a way to turn 107 m/s into 1/3 the energy.

Another thought was that at max Q, aerodynamic drag might eat up 1/3 of the thrust of the engines, especially since the main engines throttle down to 70% to avoid excessive stresses on the vehicle, but this only occurs over a brief portion of the overall flight. My best guess is that either a decimal point got misplaced or gravity losses (which tend to be about 10 times higher than drag losses) were lumped in.

Would have been gravity drag, then. Like I said, we just integrated the variable thrust over the vertical distance covered, then subtracted the kinetic and gravitational potential energy of each stage; the resulting figure was around a third of the total. But I suppose that would include both atmospheric and gravity drag. Both of which are excused by a balloon, incidentally.
User avatar
davidstarlingm
 
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC


Return to Science

Who is online

Users browsing this forum: scarecrovv and 9 guests