SpaceX News

[D Tibbets]

As a tangential consideration- I wonder if the cluster of 9 engines on the Falcon 9 has any effect of the effective nozzle exhaust expansion of the engines. Sort of like Arospike designs where performance in dense atmosphere and space both are optimized. The images of the Falcon 9 in the latter stages of boost and the spread of the peripheral plumes - and compression of the central(?) plumes versus the distinct exhausts of each engine at low altitude make me wonder if there is any partial benifit.

Also, I wonder if the engine exhaust shields on the Dragon 2 may have some Arospike like properties.

Dan Tibbets

[Skipjack]

Musk said "first stage can do SSTO without second stage and very small payload" and I don't think that that was including recovery. That would require TPS and additional fuel and other things that would probably blow the weight budget.
That was before the latest payload upgrade of the F9, though. So things might change with that.
I think that if the Raptor has an equally impressive T/W ratio of the Merlin 1D (of almost 200!!), it would be possible to have a reusable SSTO using 9 Raptors or so. That would probably be a Falcon Heavy sized rocket with a F9 sized payload to LEO. Payloads to GTO would require an extra stage.

[kunkmiester]

Such a system would be 100% reusable, making putting people and small payloads in orbit absurdly cheap. If you can get it high enough, the Draco thrusters should be plenty to maneuver to the desired orbit, and/or rendezvous with an station or ship.

An alternative design would be a tanker, intended to gas up second stages or fuel depots in orbit, and return, again reusing 100% of the rocket.

[TDPerk]

I am not sure where 550 tons comes from, that is very high (like a magnitude), unless it was a typo, and you meant 55 metric tons. http://www.spacex.com/about/capabilities

The F9 has a quoted payload to Mars of about 4.5 tons and 25 to LEO. The BFR has a goal payload to Mars of 100 tons, so if the ratio is the same, 550 tons to LEO for the BFR. Even if for some reason it's only a ratio of twice it still beats the SLS in payload and launch cost both, so the $/lb are dramatically lower. The BFR is AFAIK is a 15m diameter rocket.

Not that the SLS is hard to beat there with 5 launches planned through 2026 with system budget to that point in time of 35 billion.

[DeltaV]

If you assume a capability for stage 1 to reach a minimal orbit, it still needs to dump all of that energy upon return.

There is no chance of it surviving reentry without a Thermal Protection System (TPS), for which there is no margin. Unless...
1) Enough fuel remains to use engine exhaust plume(s) as a virtual heat shield and still have enough left for touchdown, or
2) A low-mass inflatable heat shield is deployed, or
3) A magnetic shield (along the lines of Kirtley/MSNW) with a low-mass power supply is used (MHD conversion of kinetic energy?).

[ladajo]

Therefore it would appear that they are shedding and protecting with a burn, given 8.2k km/hr, and being exo-atmosphere for seperation.

[paperburn1]

This is making quite a few assumptions but if you had a under expanded bell for the rocket motors and were willing to throw away some fuel you could do the majority of your deceleration above the atmosphere then by feeding an extra liquid oxygen to a under expanded bell it would make a relatively acceptable TPS system up to maybe 9K entry speeds (back of the envelope calculations only ) the nozzles are capable of standing quite a range of heat and with the extra oxygen for cooling it probably would make a nice virtual blunt return object. That would be some balls engineering.
Most people get hung up on the TPS thermal protection system as a single item. When reality you can use several different structures for the different phases of the recovery. So you your exhaust is a heatshield, a little bit of extra cooling provided by the liquid oxygen or fuel that is fed into the system but not burnt. The nozzles themselves are an excellent heatshield. Some metallic ceramics around the base of the motors themselves to provide the protection for ascent and descent With a little bit of active cooling and you just might have about everything you need to bring down the first stage from orbit intact. In my mind it is still critical how much energy you can shed before the actual contact atmosphere above the Kármán line at an altitude of more than 100 km (62 mi.) But still all probably very doable I'm willing to bet on musk has figured out how
\
EDIT
or maybe he is doing it this way
http://www.spacex.com/press/2012/12/19/ ... simulating
A sample of PICA-X heat shield material subjected to temperatures of up to 1850 degrees Celsius (3360 degrees Fahrenheit), at the Arc Jet Complex at NASA Ames Research Center, Moffett Field, California. The NASA-originated PICA material holds the record for high-speed reentry into the Earth's atmosphere. The SpaceX-developed and manufactured PICA-X variants meet or exceed the performance of the original material, and will protect the Dragon spacecraft on its return to Earth.

[ladajo]

For Falcon 9, it really does appear he is using the nozzles, and maybe some thrust to create a virtual shield. He doesn't have to keep it up long, just enough to drop to a regime where the steering fins can get a decent bite without shearing. Then he can use the steering to spiral brake the booster down before centering it up for the landing and final burn for touchdown.
I checked the video again, and it appears they are separating at the noted 8,300 km/hr, and 70 km altitude (about 44 miles / 230kft). Hmm...

[krenshala]

8300km/hr is a bit over 2.3km/s. It takes a minimum of ~11km/s of dV (depending on the vehicle) to reach LEO, and 200km altitude requires an orbital speed of ~7.8km/s. This means the rocket, at first stage separation, is only moving at about 1/3 to 1/4 something in LEO would be.

[Skipjack]

People generally overestimate the weight of the TPS for a VTOL SSTO. The shuttle could have gotten away with much less heavy TPS if it had not needed the height cross range. PICA-X is extremely lightweight at less than 0.25 grams per cm3. Plus an empty SSTO is very buoyant. It is more like a feather than a brick. Gary Hudson proposed active cooling (using a ton of water or so) for his Phoenix SSTO), which might be another option worth investigating.
I don't think that a F9 based SSTO would have much merit (though it would almost work), but one based on 9 Raptor engines (estimating their performance), could probably have a reasonable payload to LEO.
But, it would need an extra kick stage for GTO missions and it would not have much cross range (though they would depend as well).

[paperburn1]

Based on the number I have run and the figures I have heard L:
\GTO 160 KG
\LEO 500 KG

[kunkmiester]

I'd imagine if you can get an SSTO tanker with a decent payload, GTO and steep inclination orbits would be doable by putting the satellite in orbit, and using a booster already in orbit to put it where you want it.

[DeltaV]

People generally overestimate the weight of the TPS for a VTOL SSTO. The shuttle could have gotten away with much less heavy TPS if it had not needed the height cross range. PICA-X is extremely lightweight at less than 0.25 grams per cm3.

For a PICA shield, there is the issue of the unfavorable geometry of a separated stage 1. There are no decent aerosurfaces at the ends. The PICA would need to be wrapped around (most of) the cylinder* and used on the end, where hot spots occur. Relative wind vector would need to be kept far from the cylinder axis, unless some sort of end-protecting, PICA-covered deflector was used.

Something that might work along these lines is to have a translating interstage section that slides back to reveal a PICA-covered nose. The engine end is hopeless in this regard.

( * The cryogenic tanks make that a structural attachment challenge. Maybe PICA tiles attached to cylinder-wrapped, elastic "fishnet" in a sliding, thin-edged "shingle" arrangement.)

[ladajo]

Something that might work along these lines is to have a translating interstage section that slides back to reveal a PICA-covered nose. The engine end is hopeless in this regard.

How would you manage the pitch over maneuver once in lower atmosphere in preparation for landing? Seems like a lot of potential stress...

[hanelyp]

Weight of the engines makes it difficult getting anything similar to the Falcon9 first stage to reenter at any attitude other than tail first. One option for keeping the engines cool is running an expander cycle transpiration system: fluid through nozzle coolant passages, hot fluid powering a turbopump, then dumping through the engine to exit subsonic as a shield layer. This may need a separate turbopump for the reentry coolant cycle, running a single fluid at lesser volume. Running the engine at minimal throttle would use more propellant, but works without the extra systems.