Vacuum-optimized Dragon V2 for Falcon 9 second stage

[AngelLestat]

43 minutes ago, fredinno said:

Indeed, if it was so easy, then hypergols would not be used anymore extensively.

When you need just a little deltav and your tanks are so small (volume) than the surface is significant (volume surface relation) and when they need to be pointed to earth no matter where is the sun, then yeah.. hypergolics sounds fine in most cases when you did not bother to develope a methane engine. 

43 minutes ago, fredinno said:

Boil-off has still not been solved, and the solution you propose would be another expense added to a device that would only be used ~10 times. Not to mention it's never been tested. A better idea is sun shields, which have more experience behind them via infrared telescopes like the JWST.

I said that methane does not need active cooling.. what does means for you?  it does not need also all those things in the james webb telescope which instruments needs to be close to absolute zero, again...  we are talking about -160c!

But you ask about active cooling as it was "THE TECH", and is something super easy.

43 minutes ago, fredinno said:

I stopped answering the canadian oil pipe because it's not like you can be convinced of it anyways.

heh, is not like I present irrefutable evidence and logic..  I told you that I knew what I was talking about.  But well, I guess is not on you to recognize my time to explain you.   

[fredinno]

32 minutes ago, AngelLestat said:

When you need just a little deltav and your tanks are so small (volume) than the surface is significant (volume surface relation) and when they need to be pointed to earth no matter where is the sun, then yeah.. hypergolics sounds fine in most cases when you did not bother to develope a methane engine. 

I said that methane does not need active cooling.. what does means for you?  it does not need also all those things in the james webb telescope which instruments needs to be close to absolute zero, again...  we are talking about -160c!

But you ask about active cooling as it was "THE TECH", and is something super easy.

heh, is not like I present irrefutable evidence and logic..  I told you that I knew what I was talking about.  But well, I guess is not on you to recognize my time to explain you.   

Good lord, methane needs to be cooled, it's cryogenic, and thus boils off unless you use measures to stop/mitigate it.

I'm starting to wonder if you're just stubborn as hell, or if you're just trolling.

 

Cryogens were looked at during Apollo for the Apollo SM, and never looked at again for similar SMs for a reason. Hypergols can be stored, and can be fired as many times as you want, and are less complex (engines are essential in space).

[AngelLestat]

It needs to be cooled if the tank face the sun, or if is on earth surface, if is on space with a sunlight bloking and you have a decent insulation between the tank and your crew module, then it does not need to be cool it because space is already much colder than lox.

The future is very close.. so no sure where you will hide when arrives.

[fredinno]

3 hours ago, AngelLestat said:

It needs to be cooled if the tank face the sun, or if is on earth surface, if is on space with a sunlight bloking and you have a decent insulation between the tank and your crew module, then it does not need to be cool it because space is already much colder than lox.

The future is very close.. so no sure where you will hide when arrives.

Indeed it is close. CH4 is good for Mars if you are using ISRU- otherwise, the added risk isn't worth the slight payload advantage. I'm all for using ISRU, it's just that 70s plans never used them.

[Exoscientist]

 I've been trying to calculate how much extra fuel needs to be carried for the Dragon V2 to be able to land on the Moon. The problem is the 1,000 psi SuperDraco chamber pressure means the tank pressure has to be even higher. But tank pressure this high means you need heavy tanks to hold it. 

What's an estimate for the tank mass for hypergolics when the tank pressure is this high?

 

  Bob Clark

[kerbiloid]

On 14.03.2016 at 6:17 AM, AngelLestat said:

It needs to be cooled if the tank face the sun, or if is on earth surface

It needs to be cooled anyway. At least because you don't like the liquid methane temperature in your cabin.

Except of cryotanks, other parts of ship are warm. (Yes, -100°C is warm compared with liquid O₂ or CH₄).
Heat flows through the ship construction. Some (small) part of liquid gas gets warm and vapourizes. Vapour amount grows, its pressure grows.
You must either actively cool the tank making the vapour again become a liquid, or drain into space a small excess amount of vapour through a vent valve. You can shade it from sun, you can stir it to cool the warm piece with cold pieces, but this is unavoidable.
The more volatile is gas - the more frequently you exhaust this excess. Hydrogen is beyond comparison, of course, but any another liquified gas also does this.

Hypergolics are not so volatile and due to this they can be stored for years.

 

Edited March 29, 2016 by kerbiloid

[wumpus]

Have hybrid (solid/liquid) rockets been considered for RCS?  My guess is that they would be more for corrective burns and other things that require higher (but still moderate) Isp and fewer re-lights.  Basically they allow a broad level of temperature storage (hot rodders keep N2O under the hood of their cars.  Boiloff isn't an issue), allow easy throttle abilities and reuse.  The missing ingredient is that they aren't hypergolic and that re-lighting will probably kill any attempt for integrating them into an RCS (no matter how reliable, no part is more reliable than not needing the part in the first place).

[Basto]

57 minutes ago, wumpus said:

Have hybrid (solid/liquid) rockets been considered for RCS?  My guess is that they would be more for corrective burns and other things that require higher (but still moderate) Isp and fewer re-lights.  Basically they allow a broad level of temperature storage (hot rodders keep N2O under the hood of their cars.  Boiloff isn't an issue), allow easy throttle abilities and reuse.  The missing ingredient is that they aren't hypergolic and that re-lighting will probably kill any attempt for integrating them into an RCS (no matter how reliable, no part is more reliable than not needing the part in the first place).

Hot rodders are not using NO2 as their sole oxidizer for combustion but to enhance a ready supply. The reason you want your fuel/oxidizer really cold is you can fit more of it in a smaller space at lower pressures. 

[wumpus]

58 minutes ago, Basto said:

Hot rodders are not using NO2 as their sole oxidizer for combustion but to enhance a ready supply. The reason you want your fuel/oxidizer really cold is you can fit more of it in a smaller space at lower pressures. 

They *are* storing it as a liquid (and getting the cold effects as it boils when used).  The whole point is that you don't *want* any fuel that *has* to be that cold (a good part of the reason that hypergolics are still used).  Also it has been used as the sole oxidizer by space ship one (but not two/three) and plenty of amature rockets.

[Basto]

31 minutes ago, wumpus said:

They *are* storing it as a liquid (and getting the cold effects as it boils when used).  The whole point is that you don't *want* any fuel that *has* to be that cold (a good part of the reason that hypergolics are still used).  Also it has been used as the sole oxidizer by space ship one (but not two/three) and plenty of amature rockets.

Actually I think you are confusing liquified compressed gas with cryogenically liquified the gas. 

Liquified compressed gasses are in a liquid form at ambient temperature and are only in a liquid state because of the pressure applied to them.  Yes you could use NO2 as an oxidizer and in an amateur rocketry perspective I am sure it works great. 

But it you want to fit a ton of oxidizer/fuel in a very small space you can either raise the pressure to ridiculous amounts requiring extremely thick walled pressure vessels to contain it. Or you can lower the temperature cryogenically allowing you to cram in more at lower pressures (i.e. Falcon FT). The boil off issue is if you allow the cryogenic gas to boil and either don't vent it or find some way to cool it back down your tank will explode from the pressure. 

[fredinno]

5 hours ago, wumpus said:

Have hybrid (solid/liquid) rockets been considered for RCS?  My guess is that they would be more for corrective burns and other things that require higher (but still moderate) Isp and fewer re-lights.  Basically they allow a broad level of temperature storage (hot rodders keep N2O under the hood of their cars.  Boiloff isn't an issue), allow easy throttle abilities and reuse.  The missing ingredient is that they aren't hypergolic and that re-lighting will probably kill any attempt for integrating them into an RCS (no matter how reliable, no part is more reliable than not needing the part in the first place).

As far as I know, not seriously. I mean, you'd need to carry solid propellant every place there is a need for an RCS motor, or try using it as a granulated powder pushed through a pipe.

 

The former is problematic, as you often need RCS motors where there is little extra space to work with (like the Orion CM), and the latter has very little experience behind it.

Engines are expensive, so the notion seems to be "if it's not broken, don't fix it."

[wumpus]

4 minutes ago, fredinno said:

As far as I know, not seriously. I mean, you'd need to carry solid propellant every place there is a need for an RCS motor, or try using it as a granulated powder pushed through a pipe.

 

The former is problematic, as you often need RCS motors where there is little extra space to work with (like the Orion CM), and the latter has very little experience behind it.

Engines are expensive, so the notion seems to be "if it's not broken, don't fix it."

The suggestion was made for something closer to the Shuttle's OMS system.  That thing provide 1000lbs of propellant as part of an RCS.  You wouldn't want to have to burn such a thing for every rotation, but you also wouldn't want to generate any significant delta-v with most RCS.

[fredinno]

45 minutes ago, wumpus said:

The suggestion was made for something closer to the Shuttle's OMS system.  That thing provide 1000lbs of propellant as part of an RCS.  You wouldn't want to have to burn such a thing for every rotation, but you also wouldn't want to generate any significant delta-v with most RCS.

Yeah, and if you wanted to use the same system for RCS, you need solid fuel at every RCS nozzle.

Using it for OMS is a little more reasonable- however, why you would use that instead of Hydrogen Peroxide, or https://en.wikipedia.org/wiki/Nitrous_oxide

which have a lot more experience behind them, and are also non-toxic and monopropellant, is up to serious question.

[kerbiloid]

4 hours ago, fredinno said:

Yeah, and if you wanted to use the same system for RCS, you need solid fuel at every RCS nozzle.

Using it for OMS is a little more reasonable- however, why you would use that instead of Hydrogen Peroxide, or https://en.wikipedia.org/wiki/Nitrous_oxide

which have a lot more experience behind them, and are also non-toxic and monopropellant, is up to serious question.

Also they can drink Hydrogen Peroxide (of course, not directly) and breathe it. Because → water + oxygen.

Edited March 30, 2016 by kerbiloid

[fredinno]

4 hours ago, kerbiloid said:

Also they can drink Hydrogen Peroxide (of course, not directly) and breathe it. Because → water + oxygen.

I don't like hydrogen peroxide though, for that very reason- it slowly decays. I can't find the rate of decay in standard temperature and pressure though.

[kerbiloid]

8 hours ago, fredinno said:

I don't like hydrogen peroxide though, for that very reason- it slowly decays. I can't find the rate of decay in standard temperature and pressure though.

Page 4

[fredinno]

1 hour ago, kerbiloid said:

Page 4

Ah, thanks. It's not that much worse than boil-off then, I guess...

[Exoscientist]

 I'm glad you see the usefulness of altitude compensation. Try calculating what payload the F9 FT first stage could get as an expendable SSTO using altitude compensation. I think you'll be surprised.

 

  Bob Clark

[KSK]

On 11/03/2016 at 1:23 PM, Steel said:

My question is, other than not throwing away on Merlin 1D each launch, what do you gain?

That's what I'm wondering too. Sure - not throwing away that engine would be nice but is it worth the expense of redesigning a working booster, redesigning the Dragon 2, re-certifying both designs and dealing with very large quantities of unpleasant hypergols? My guess is probably not.

Also, at the moment, there is quite a lot of commonality between the propellant tanks on both of the F9 stages which helps keep manufacturing costs down. Unless you can use the same tank design for storing and using hypergols as you can for kerolox (which seems unlikely to me but I don't have a sound basis for that), then SpaceX would need a separate production line for its upper stage tanks, which would add expense.

Finally - and I'm really reaching into areas of personal non-expertise here, so this may be a load of baloney - but replacing the current upper stage with your hypergol drop tank could change the mass distribution along your rocket quite substantially, unless the drop tanks are the same height as the current upper stage and the hypergols have the same density as kerosene/LOX. That sounds as though it could change the vibration modes of that rocket quite a bit, leading to possible structural problems, pogo problems and a bunch of other things that I don't even know about.

Insert obligatory 'real life rocketry isn't like KSP' comment here.

With all that said, it's a neat idea but I think one which is probably outweighed by its operational drawbacks.

Edited May 3, 2016 by KSK