Space Ship Two - General Thread

[kevin-rf]

VG and not Scaled?

[Chandonn]

Let me channel Jim here:  spacexraft and rockets are not legos...

[Nomadd]

The obvious deal would be between SpaceX and VG/Scaled, where SpaceX would provide Kestrel engines to VG, and VG would provide composite structures for SpaceX. Yeah, I know that use of Kestrel would require a redesign for SS2, but the performance would be through the roof.

 When you're trying to push a 22,000 lb craft near vertical I don't think a 6,800 lb motor is going to work too well. They need around 36,000 lbs of thrust. And replacing a tank of nitrous and a big pencil eraser (tiny exaggeration) with a real rocket engine probably wouldn't do their business model much good.

[Danderman]

Let me channel Jim here:  spacexraft and rockets are not legos...

Jim is correct. I did mention the word "redesign". Normally, redesigns are not a good thing, but I am writing in the context of the rumor of there being a "fatal flaw" in the SS2 hybrid motor.

[Malderi]

I'm still extremely curious why they decided to go with a hybrid motor. Not many applications use them, so what's different about SS1/SS2 in particular that they thought it would be worth it (as opposed to a solid or reusable liquid design)?

[docmordrid]

At the least - others fill the gaps please

Vs. Solids: the burn can be aborted and it's potentially throttleable

Vs. liquids: simpler, possibly cheaper and with nitrous oxide no cryogenics

[Malderi]

I understand those advantages. But, the fact remains that very few other vehicles have used hybrid motors. SS1/SS2 are pretty unique vehicles, however, so it may just be the combination of manned/suborbital that means it makes sense.

No need for sounding rockets, etc., to abort a burn, because whether it blows up or falls gracefully into the ocean, it's still a lost payload.

[kevin-rf]

I understand those advantages. But, the fact remains that very few other vehicles have used hybrid motors. SS1/SS2 are pretty unique vehicles, however, so it may just be the combination of manned/suborbital that means it makes sense.

Might be worth noting that the X-15 used a combo of used ammonia and liquid oxygen. I don't know of any rocket that used that mix... This reusable suborbital stuff puts some pretty interesting constraints on the vehicle.

[HMXHMX]

I understand those advantages. But, the fact remains that very few other vehicles have used hybrid motors. SS1/SS2 are pretty unique vehicles, however, so it may just be the combination of manned/suborbital that means it makes sense.

Might be worth noting that the X-15 used a combo of used ammonia and liquid oxygen. I don't know of any rocket that used that mix... This reusable suborbital stuff puts some pretty interesting constraints on the vehicle.

And no one ever used ammonia again in the U.S.  It was a beast of an engine to tame.  And the fuel is nasty. 

Read the story in John Clark's Ignition.

For a liquid bi-propellant, the best propellant choices – in my view – are LOX-LNG or LOX-Kerosene.  I far prefer the former to the latter, for smooth burning, "green" cred (a factor for VG, since they have made such a  big deal out of the "green" features of the Nitrous hybrid) and cost.

[mmeijeri]

And no one ever used ammonia again in the U.S.  It was a beast of an engine to tame.  And the fuel is nasty. 

I thought it was relatively benign, and therefore a poor man's hydrazine. Isn't it used on farms?

Read the story in John Clark's Ignition.

Wouldn't the combustion stability problems be helped by using hydrogen peroxide as the oxidiser?

For a liquid bi-propellant, the best propellant choices – in my view – are LOX-LNG or LOX-Kerosene.  I far prefer the former to the latter, for smooth burning, "green" cred (a factor for VG, since they have made such a  big deal out of the "green" features of the Nitrous hybrid) and cost.

Why LNG? I thought you were a fan of propane.

[kkattula]

For a liquid bi-propellant, the best propellant choices – in my view – are LOX-LNG or LOX-Kerosene.  I far prefer the former to the latter, for smooth burning, "green" cred (a factor for VG, since they have made such a  big deal out of the "green" features of the Nitrous hybrid) and cost.

Or there's LOX-Ethanol and LOX-IPA.  (As used by Armadillo & Marsten respectively) Easier to deal with than LNG, and cleaner for multi-use engines than kero. Slightly lower performance, but more than enough for this purpose.

On the other hand, Scaled's 'semi-competitor' XCOR are going with LOX-Kero.

All these choices would require major tank & airframe re-design.  I did read a suggestion under that report that the nitrous tank would hold the right proportion of H202, to fuel (kero?) in several pencil tanks where the hybrid grain sits.

[HMXHMX]

And no one ever used ammonia again in the U.S.  It was a beast of an engine to tame.  And the fuel is nasty. 

I thought it was relatively benign, and therefore a poor man's hydrazine. Isn't it used on farms?

Read the story in John Clark's Ignition.

Wouldn't the combustion stability problems be helped by using hydrogen peroxide as the oxidiser?

For a liquid bi-propellant, the best propellant choices – in my view – are LOX-LNG or LOX-Kerosene.  I far prefer the former to the latter, for smooth burning, "green" cred (a factor for VG, since they have made such a  big deal out of the "green" features of the Nitrous hybrid) and cost.

Why LNG? I thought you were a fan of propane.

NH3 may be used in many applications, but it still is toxic at high concentration, and leaks will produce a more "unpleasant experience" for one's customers than hydrocarbon alternatives.

I don't know of engines with H2O2-NH3 as a propellant, so can't speak to the combustion issues, but the Bell XLR-99 had a long development struggle.  Speaking only personally, I wouldn't attempt an engine development with NH3.

Propane is good, too.  I currently favor LNG for temperature compatibility with LOX, and the availability of at least one pump fed engine that can burn it.

[HMXHMX]

For a liquid bi-propellant, the best propellant choices – in my view – are LOX-LNG or LOX-Kerosene.  I far prefer the former to the latter, for smooth burning, "green" cred (a factor for VG, since they have made such a  big deal out of the "green" features of the Nitrous hybrid) and cost.

Or there's LOX-Ethanol and LOX-IPA.  (As used by Armadillo & Marsten respectively) Easier to deal with than LNG, and cleaner for multi-use engines than kero. Slightly lower performance, but more than enough for this purpose.

On the other hand, Scaled's 'semi-competitor' XCOR are going with LOX-Kero.

All these choices would require major tank & airframe re-design.  I did read a suggestion under that report that the nitrous tank would hold the right proportion of H202, to fuel (kero?) in several pencil tanks where the hybrid grain sits.

Once you go cryogenic for the LOX, no reason not to do so for the fuel, too.  But there are many ways to fix SS2's propulsion problem, once the decision becomes "use liquids."

[docmordrid]

What about NOFBx? Single (existing?) tank, etc.

[HMXHMX]

What about NOFBx? Single (existing?) tank, etc.

It's an interesting option, but there's no engine in the thrust class SS2 requires – at least at this time.

What VG needs is a near-term alternative to the hybrid.

[docmordrid]

Hmmmm....a 2009 proposal for NOFBx Mars ascent. Wonder if it's hiding in someones barn?

http://sbir.gsfc.nasa.gov/SBIR/abstracts/09/sbir/phase2/SBIR-09-2-S3.08-8305.html?solicitationId=SBIR_09_P2

[Rocket Science]

I guess they could consider the old XLR 11 twin pack like in the X-15...
http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=889

[Patchouli]

I guess they could consider the old XLR 11 twin pack like in the X-15...
http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=889

Another potential replacement would be the CHASE-10 methane engine it's in the RL-10 thrust class or about 22,000lbs.
The ISP is about 100 seconds higher then the hybrid rocket which should allow similar performance even with a non optimal tank design.

[Rocket Science]

Very nice... two of those would be even sweeter...

[HMXHMX]

Very nice... two of those would be even sweeter...

It would take at least two, possibly three, and would be my engine of choice for the job, all things considered.