I'm curious in general about how feasible it is to put a single full-size, vacuum-optimised engine on the rear end of a second stage, and a small-scale, sea-level/supersonic-retropropulsion-optimised engine on the forward end? (all using the same fuel/oxidiser tanks - no flip and burn maneuvers - land it "upside down").
I just figure if boost stage engines and vacuum engines have their own optimisations, surely supersonic retropropulsion/landing engines would have their own, separate optimisations.
I'm curious in general about how feasible it is to put a single full-size, vacuum-optimised engine on the rear end of a second stage
The easiest way is to use a slightly modified ITS with sea nozzles acting as a booster. The passenger and cargo replaced by an empty bay with top doors a la shuttle (same external ITS shape). During launch, at certain altitude, doors open to deploy a 2nd stage with 1 raptor + payload without fairing. After deployment, booster close doors and return to launch site.
Composite airframe, self pressurized, recoverable conventional fairing. Loss of payload capacity with a connected cargo space would probably be too high. Steering during reentry with flaps, similar to ITS and IXV.Lifting body?Edit: This would test many of the technologies needed for ITS. Maybe even refuelling, which might enable cargo moon landing.
The easiest way is to use a slightly modified ITS with sea nozzles acting as a booster. The passenger and cargo replaced by an empty bay with top doors a la shuttle (same external ITS shape). During launch, at certain altitude, doors open to deploy a 2nd stage with 1 raptor + payload without fairing. After deployment, booster close doors and return to launch site.Would have around 28-29MN compared to the 23 of FH, allow to test the infrastructure for Mars with revenue using a configuration very close to the well known F9.Specific developments are the fairing-doors, the deployment mechanism and the 2nd stage. The commonality advantages with the Mars architecture are huge, allow for testing small scale without an entire new vehicle.
Opening doors while ballistic to release a second stage? Seems like everything has to work in a very delicate, highly choreographed, series of actions or else you lose the booster or the second stage or both. (I'm assuming with a door failure to open the booster can't land, not enough fuel remaining)I confess I'm highly dubious of any intermediate vehicles, with the possible exception of a raptor second stage for F9/FH (which I am still dubious of but not highly dubious )... but we'll find out soon, maybe.
Quote from: mikelepage on 04/23/2017 07:47 amI'm curious in general about how feasible it is to put a single full-size, vacuum-optimised engine on the rear end of a second stage, and a small-scale, sea-level/supersonic-retropropulsion-optimised engine on the forward end? (all using the same fuel/oxidiser tanks - no flip and burn maneuvers - land it "upside down").I am continuous baffled by that idea. You need one end with a heat shield to reenter. How would an engine survive there without complex mechanisms to protect it, which are failure points and added complexities?
The second stage re-enters on its belly using split flaps for attitude control, like the ITS Spaceship and Tanker. However, it has no landing legs near its tail, and no tail auxiliary thrusters. Instead, panels on the underside open up, both serving as landing skids and exposing auxiliary landing thrusters for a propulsive belly-first landing:I've worked out all the specs...filled up about three Excel spreadsheets doing so, too.First stage dry mass: 17 tonnesFirst stage propellant: 421 tonnesFirst stage mass ratio: 24:1Thrust at launch: 6,266 kNSecond stage dry mass: 6.6 tonnesSecond stage propellant: 141 tonnesTotal vacuum thrust: 2,292 kNReusable payload to LEO: 24 tonnesReusable payload to GTO: 6.8 tonnesDownmass from LEO: 22 tonnes
Quote from: sevenperforce on 04/23/2017 06:46 pmThe second stage re-enters on its belly using split flaps for attitude control, like the ITS Spaceship and Tanker. However, it has no landing legs near its tail, and no tail auxiliary thrusters. Instead, panels on the underside open up, both serving as landing skids and exposing auxiliary landing thrusters for a propulsive belly-first landing.I've worked out all the specs...filled up about three Excel spreadsheets doing so, too.First stage dry mass: 17 tonnesFirst stage propellant: 421 tonnesFirst stage mass ratio: 24:1Thrust at launch: 6,266 kNSecond stage dry mass: 6.6 tonnesSecond stage propellant: 141 tonnesTotal vacuum thrust: 2,292 kNReusable payload to LEO: 24 tonnesReusable payload to GTO: 6.8 tonnesDownmass from LEO: 22 tonnes Cool factor is high but how did you work out the second stage dry mass? Wouldn't the lower surface area of a smaller craft during reentry mean higher g-forces, greater loads, and more need for structural reinforcement? Seems a little light to me...
The second stage re-enters on its belly using split flaps for attitude control, like the ITS Spaceship and Tanker. However, it has no landing legs near its tail, and no tail auxiliary thrusters. Instead, panels on the underside open up, both serving as landing skids and exposing auxiliary landing thrusters for a propulsive belly-first landing.I've worked out all the specs...filled up about three Excel spreadsheets doing so, too.First stage dry mass: 17 tonnesFirst stage propellant: 421 tonnesFirst stage mass ratio: 24:1Thrust at launch: 6,266 kNSecond stage dry mass: 6.6 tonnesSecond stage propellant: 141 tonnesTotal vacuum thrust: 2,292 kNReusable payload to LEO: 24 tonnesReusable payload to GTO: 6.8 tonnesDownmass from LEO: 22 tonnes
EDIT ps: talking to the Armadillo Aerospace guys 10 years ago at XPrize cup 2007 I asked why they went with VTVL rather than VTHL (dreamchaser type vehicles), and the answer they gave was mainly along the lines of "you wouldn't believe how much extra mass you add when the airframe has to support/propel itself in two different orientations". I was reminded of that during the ITS presentation - the ship performs entry and descent on its belly, but flips up to land on its tail... seems like a risky maneuver that you wouldn't make unless it was absolutely necessary.
SpaceX has said Falcon Heavy is "hard". A 9 Raptor engine 7m diameter reusable first stage, with a single engine vacuum Raptor second stage. Add a few small landing thrusters for second stage after re-entry. This single stick two stage rocket would replace Falcon Heavy and be able to test all factors of in a reduced scale. Like the previous poster, possibly a mini-ITS half scale, but with a single stick 9 engine raptor first stage. This would make for a completely reusable two stage vehicle. F9/FH is too small a diameter and too tall for a good mini-ITS. After sea level Raptor is developed, a single stick upscaled F9 to 7m diameter shouldn't be a problem except location of the manufacturing facility. This new rocket would be slightly more powerful than BO's New Glenn, and be fully reusable.
A 6 Raptor booster would slightly more powerful than New Glenn. A 9 Raptor version considerably more so.I do think that mini-ITS on FH is feasible, though, since I believe the biggest structural issue with Falcon Heavy is how fast it goes in the dense lower atmosphere. A heavier upper stage means Max-Q and trans-sonic regions are higher up in thinner atmosphere with less dynamic stress, and the rocket goes through high altitude wind shear much slower. It also means that staging is lower and slower so it's easier to get the boosters back.
Another option is a second stage for FH as a half scaled ITS. 6m diameter, 24m long, 1 raptor and 3 flavours:1- Cargo version with integrated fairing (crocodile style) to deploy satellites2- Mini crewed ITS launched as FH: minibus of 20 PAX to LEO, 10 PAX to moon vicinity and 5 to asteroids or even Phobos. Crewed part is 6m diameter, 9m long with around 180m3. Could copy-paste beefed up ECLSS systems from Dragon and become a very polyvalent spaceship.3 - Tanker versionThat would be the spaceship that NASA needs for BLEO and would match beautifully with the SLS. But I guess reminds too much the shuttle. Would delay too much the bigger brother, but a very good exploration spaceship.