sevenperforce

Boots on the moon by 2020 is easy enough if you really wanted to do it. Two Falcon Heavy launches and a redesigned Dragon 2 is all you need. Getting to Mars by 2020? Well, what would we need? One F9 Dragon 1 launch to send supplies to the ISS along with a BEAM. One Delta IV Heavy launch to send Orion to the ISS. One SLS launch to send a custom-built, rigid utility tunnel/docking adapter to the ISS. One F9 Dragon 2 launch to send the crew to the ISS along with a second BEAM. Another SLS launch to send the cryogenic propulsion stage to the ISS. With assembly at the ISS, that's enough for getting crew to Martian orbit and back. For landing, you'd need a Falcon Heavy launch of Dragon 2 to Mars orbit. You might need a methalox upper stage to go along for the ride and execute a propulsive orbital insertion. For Mars ascent, you'd need either FH+Raptor US or a three-stage New Glenn to send a custom MAV to the Martian surface...maybe something like Mid-L/D.

Do NOT make this political. Use passive voice if you must. Funding has been authorized for a manned Mars mission by 2030, but plans have recently been suggested for a manned Mars mission as early as 2020. Without ANY discussion of who authorized funding or who suggested the earlier timeframe...discuss. Is it possible to put flags and footprints on Mars with a launch in December 2020? In theory, maybe. There's no way we could possibly do this in a single launch -- there's no vehicle nearly large enough -- so it would have to go in piecemeal with Mars Orbit Rendezvous. Launch an MAV to Mars with one vehicle, launch a Mars Descent Vehicle with another vehicle, and then launch the crew in a transfer vehicle which doubles as the Earth Re-entry vehicle in a third launch. Falcon Heavy can send an uncrewed Dragon 2 into Martian orbit for the descent. SLS can send the crew on Orion. Nothing that can really serve as an MAV, that I can think of....

The booster does not provide much of the dV to orbit, but it provides a great deal of the energy to orbit, because it accelerates the fuel of the second stage. According to the pricing page on the SpaceX website, where standard prices are quoted assuming reuse, FH can put 8.0 tonnes into GTO with full recovery. I'll use that as a starting point for everything else. According to the SpaceX website, F9 can put 22.8 tonnes of payload into LEO expendable, while FH can put an ungodly 63.8 tonnes into LEO expendable. S2 dry mass is 4 tonnes and fuel load is 107.5 tonnes. Thus, for expendable launches, the F9 second stage provides 5.5 km/s while the FH second stage provides just 3.2 km/s. FH staging velocity is 2.3 km/s higher than F9. For GTO, F9 can put 8.3 tonnes into GTO while FH can put 26.7 tonnes into GTO, both expendable. So the second stage provides 7.8 km/s for F9 GTO and 5.1 km/s for FH GTO. FH staging velocity is 2.7 km/s higher than F9. But that's all expendable. What about recoverable launches? Well, we know that the F9FT managed to put the 5.5-tonne SES-10 into GTO with (yay reused!!) core recovery at a staging velocity of 2.28 km/s; this was likely the upper limit of F9 FT's performance (in fact, SES-10 was originally planned to go up on FH). The F9 S2 delivered a whopping 8.6 km/s of dV to the satellite. In contrast, Echostar XXIII's staging velocity was 2.7 km/s. In order to reach the same (approximate) orbit as SES-10, the second stage needed to give it 8.2 km/s. By my numbers, this puts Echostar's mass at 6.8 tonnes. This information allows us to estimate how much dV the first stage for the SES-10 launch reserved. Using vacuum isp and treating SL isp losses as an additional source of dV drag, the dV delivered by the first stage in the Echostar 23 launch was 4.17 km/s, meaning total drag losses (gravity, air, and isp) were 1.47 km/s. This means the SES-10 first-stage booster delivered approximately 3.75 km/s in dV including losses; it would have had 21.6 tonnes of propellant remaining, representing about 2.1 km/s of dV for the empty first stage. So what does it look like when Falcon Heavy puts 8 tonnes into GTO with full core recovery? Well, that's 7.8 km/s of dV for S2, meaning that it needs to be staged at 3.1 km/s. In order to survive the same re-entry profile as the SES-10 booster, the core will need to burn off 0.82 km/s of dV more than SES-10 did, so it needs to reserve about 35.7 tonnes of propellant.

The froth is mostly microbubbles...not enough to significantly lower density.

Please for the love of all that is good and holy, don't make this political.... ...but in his live phone call with the ISS astronauts, Trump stated he is not satisfied with NASA's plan to put astronauts on Mars by 2030 (a plan he just recently signed funding for) and instead wants astronauts on Mars by the end of his first term, in 2020. Thoughts?

Hmm, very nice! Reminds me of SLS, but with wings added to the core and a side-slung payload. Does the core go all the way to orbit but simply not circularize? How much dV does the side-slung vehicle carry? What kind of staging/recovery are you thinking? Another note is that with Falcon 9 and Falcon Heavy, we already have fully-reusable first stages. So all you need for a fully reusable launch system would be a fully-reusable drop-in replacement for the F9/H second stage. Might be a probable test bed for Raptor and ITS. I know my concept from the first page could definitely be dropped-in on the Falcon Heavy.

I doubt this would be an issue in a powered ship wake, but I know this is the reason why a sinking ship can cause lifeboats in its vicinity to sink. As the bulkheads rupture and other trapped air is released, it lowers the effective density of the water above it and so buoyancy fails. No sucking vortex though.

A capsule with pusher-style LES has the advantage of being able to act as a lifeboat if the orbiter is damaged on launch or in LEO. It can also abort on landing if there's a problem. Sitting around for the gantry tower to pick you up would be a bit unpleasant, though.

They are using Thiacom-8 and one other (maybe CRS-9) as the side boosters for the inaugural Falcon Heavy flight. Any ideas for a drop-in recoverable second stage...for Falcon 9 or any other launch vehicle?

Rhombus was always a nice concept -- beats out SERV handedly by using recoverable drop tanks and not worrying about the landing turbojets. Did it have any crew+cargo option? And what about LES?

WHY CAN I NOT LIKE ANY OF THESE

Agreed, since I cannae like. Of course, if the first flight of SLS goes boom, it's probably curtains for the program whether there is crew on it or not.

Discussion of Russian vs US launch vehicles and Buran vs Shuttle vs Soyuz got me thinking. I'm sure all of us here are well aware that the Shuttle program was based on some ill-conceived notions, both with respect to the demand for flights as well as the capability of NASA to execute rapid Shuttle turnaround. The Shuttle had some neat capabilities (launching payload along with service crew, e.g. Hubble) and promised abilities (sat recovery), but it was never really used like it could have been. And the flight rate was so low that reuse cost more than it saved. But what if they had been right about the demand for the Shuttle's abilities? What if the market demanded a launch vehicle that could sent up large payloads along with crew, as well as occasionally retrieving sensitive cargo from orbit? What if the market was so saturated with demand that economies of scale were in full swing? It's clear that even under those circumstances, the Shuttle's high refurbishment cost and lengthy turnaround time wouldn't have been the best fit (even ignoring its safety record). But what might have been better? If you were designing a launch vehicle with these sorts of target capabilities, how would you go about it?

I just really can't see SLS being used for...anything, really.

WHY AM I OUT OF LIKES Although I must say I prefer expendable launchers to expandable ones.

Oh, I know; I was just wondering if DECQ was proposing an identical stack or if he has any suggested improvements. That's GLOW for each version, not payload for each version. F9FT certainly is not putting 550 tonnes into LEO.

There's a splendid blending of graceful awe and stunning complexity with a liquid-flyback-booster stack. Though I think the payload-to-dry-mass ratio is...not great. How would you choose engines/body/fuel types/etc.?

At least until McDonald's can figure out a way to put it into a sandwich.

Not even close. If you divide the total number of deaths attributable to nuclear power to the total amount of energy it has produced, it is orders of magnitude safer than any other major power source. Keep in mind that coal-powered plants operating at minimum pollution levels still release more radioactive material into the environment than nuclear reactors.

With all respect...no. There are many areas of inquiry in which our feelings about what "matches the evidence" happen (coincidentally) to line up with reality, but that is not how science (or spaceflight) are conducted. If you "feel" that thrusting radially "ought" to increase your apogee, or that thrusting prograde "ought" to get you closer to another ship in front of you, orbital mechanics will correct your feelings rather hastily. The scientific consensus concerning anthropogenic climate change is based on the product of rigorous, peer-reviewed scientific research. Climate change denial might not be as inane as Flat Earth nonsense or young-Earth creationism, but it's every bit as foolhardy as insisting that smoking doesn't cause cancer.

Elon said that the ITS Spaceship and Tanker will both use split body flaps to control roll and pitch during re-entry. It will have plenty of yaw authority from its auxiliary thrusters. One nice thing about using a biconic re-entry is that you do get substantial body lift, which is AOA-dependent. So there's an element of pitch self-correction in the overall design: if your COM is farther back than it should be and it kicks your nose up, your lift increases, which raises your altitude and decreases your drag, allowing you to pitch back forward. Split flaps are best at giving roll authority, perhaps aided by auxiliary thrusters, so hypersonic attitude control shouldn't be too difficult to manage. With my design, it might even be possible to actuate the four underside panels differentially to provide the same sort of attitude control. If not, split flaps on the tail would do the job well enough. The overall aerodynamic design would most likely be tuned to passive re-entry with a crewed-version mass distribution, since that's the one version you are most concerned about re-entering safely. The cargo version would rely more heavily on the split flaps or actuated panels. My mass-fraction numbers may be slightly optimistic, but I don't think so. At least, they're no more optimistic than Elon's structural mass numbers for the ITS system. I filled up about three Excel spreadsheets making sure all the math came out right. For structural mass, I took middle-of-the-road estimates for dry mass on the Raptor engines, adjusted based on TWR for the Vacuum Raptors, deducted total engine mass from the quoted ITS system dry masses, and used that as the structural/tankage mass. I took appropriate square-cube reductions and I added in my engines and my auxiliary thrusters on top of the calculated dry mass for the smaller vehicle. Just shy of 12 km/s. No, really. With the structure alone as the payload and a full tank in LEO, it would have a whopping 11.678 km/s of dV. Of course, actually having positive payload is important. With LEO refueling it could deliver 19.2 tonnes to the lunar surface one-way or a more modest 7.6 tonnes round-trip. That 381 seconds of ISP, along with the really good tankage ratio of composites, can do a lot. I mentioned this before, but the placement of the auxiliary thrusters within the wings means that the ship can land on unprepared surfaces with relative safety, since the thruster wash doesn't impinge on the ground nearly as harshly as with more conventional landing systems. I try not to succumb to Rule of Cool too often, but I couldn't resist this. Mostly because it does genuinely offer some real advantages. And, good grief, who doesn't want to see a sleek spaceship rise straight off the lunar pad on thrusters, rotate gently to orient properly, and then fire up its big engines in the back to blast into orbit? It's exactly how the Millennium Falcon takes off. I set the total auxiliary engine thrust high enough to allow the same vertical takeoff on Mars, which (coincidentally) is precisely what you need for a nice tight landing on Earth. One thing I'm unsure of is the pressurization issues for the auxiliary thrusters. They are autogenously pressurized off the main Raptors, so I'm not sure how much dV they can push before they start to lose tank pressure.

About what I expected. If we could make a tank out of woven carbon nanotubes or straight-up graphene, then yes, high-pressure GH2 would be the way to go. But we can't...not yet, anyway. So until then, we're stuck with liquid hydrogen.

Recovery mode for the second stage is the tricky part.

Liquid mercury, maybe.

Landing on the tail (e.g., ITS Spaceship/Tanker) isn't possible because the smaller vehicle only has the high-thrust vacuum-expanded engines in the tail. You could put thrusters in the tail, but there isn't a lot of space back there, and you run the risk of damage to the engine bells, either from plume impingement or from debris being kicked up. The tail-first landing also requires very large fold-out landing legs to clear the engine bells. Landing on the nose might work a little better, but it isn't suitable for manned launches for several reasons. First, emergency abort during landing isn't possible if you're coming down cabin/capsule-first. Next, there is an increased tip-over risk. Finally, there's no seating arrangement which can support rear g-forces during launch and forward g-forces during landing. Coming down like a modern-scifi spaceship is by far the safest and most stable landing mode.