SpaceX News

[happyjack27]

No, musk needs two stages because at first you need a lot of thrust-to-mass-ratio so you need a lot of engines, and then for the rest of your trip you barely need any thrust-to-mass-ratio so you barely need any engines.

The point was that he wants to send a very large payload (larger than any before) to mars and he only has a perfect launch window every two years (when mars is closest). For operations in earth orbit and even smaller scale missions BEO, an SSTO based on the tanker ITS would be more economic.
The reasons for that are that a smaller SSTO RLV has less maintenance (no staging needed) and can fly more often with a large variety of payloads (e.g. other commercial payloads). There is no standing army of engineers waiting 2 years between flights until mars is back close to earth. The ITS has little use beyond mars colonization. You might be able to launch a couple to serve as large space stations or maybe a lunar base. But that is about the extent of what they are useful for. The same goes for the booster. So I am saying scrap the booster, change the 6 vacuum Raptors on the tanker ITS to a version that is closer to the sealevel one, replace the cargo- fuel tank with a payload shroud. And you have an SSTO RLV with the payload of a falcon 9 1.1 (or more). Enough to mount a full Dragon2 and launch astronauts to ISS for 600k each. Would probably get better/cheaper over time. Same goes for cargo. For GEO and BEO missions, use multiple launches, orbital tugs and dedicated space craft that may be assembled in orbit. Even 20 launches of this SSTO RLV would still be cheaper than a single F9 launch is now. So there is no economic argument against orbital assembly with the exception if want to launch a huge amount of mass at once to a single destination. Anyway, I hope that Musk considers building this SSTO based on the ITS. If not, maybe they would sell a version of the ITS to 3rd parties. At less than 2.4 million a launch, I am sure that there are quite a few that would love this sort of capabilities. The military for sure is one.

to get a transport up to orbit, you need more engines on it, and that means you're going to need more fuel. by the time you've done all that, with enough extra thrust to carry a payload, what you have is a tanker, that can only get to leo, which is just as well because its poorly optimized for interplanetary - its got way too many engines.

[Skipjack]

to get a transport up to orbit, you need more engines on it, and that means you're going to need more fuel. by the time you've done all that, with enough extra thrust to carry a payload, what you have is a tanker, that can only get to leo, which is just as well because its poorly optimized for interplanetary - its got way too many engines.

I think you were misunderstanding me. I was not talking about using the proposed SSTO for interplanetary transport. Let me try to explain again:
The full BFR- ITS stack (of booster and ITS) would be overkill for anything but colonization or large scale BEO missions. You rarely need to launch hundreds of tons into a single LEO and that mass to the moon only makes sense if you plan to have a colony there. The ITS in its current configuration really is only good to transport 100 people or the equivalent in cargo (most of it pressurized too) or as a self transporting outpost. If you landed it on the moon, you would have an instant moon village there. But the technology could be adapted to have a launch vehicle with less payload, but less maintenance and a higher launch cadence.
The tanker can launch on its own in its current configuration all the way to orbit, but without any payload. Not even in this configuration would you need to add extra engines for it to work as an SSTO.
But in its configuration as a second stage it is badly optimized to be an SSTO because most of its engines are for vacuum use only. Replace them with engines that are half way between LEO and vac and thus can be used right from takeoff and you have a much more capable LV. The smaller engine bells will probably safe some weight too which would directly translate into more payload. Then add a payload shroud instead of the tanker tank and the result is an extremely cheap (less than 2.4 million per launch), low maintenance SSTO that can have a payload of roughly Falcon 1.1 (or more, some estimates go up to 40 tonnes) to LEO.
For anything beyond LEO, you would probably assemble a dedicated spacecraft in orbit or do on orbit refueling for some mission profiles like to GEO or maybe even to lunar orbit. The point is that you now have options.

[Diogenes]

Implication of sabotage adds intrigue to SpaceX investigation

About two weeks earlier, one of SpaceX’s rockets blew up on a launchpad while it was awaiting an engine test. As part of the investigation, SpaceX officials had come across something suspicious they wanted to check out, according to three industry officials with knowledge of the episode. SpaceX had still images from video that appeared to show an odd shadow, then a white spot on the roof of a nearby building belonging to ULA, a joint venture between Lockheed Martin and Boeing.

https://www.washingtonpost.com/business ... story.html

[happyjack27]

to get a transport up to orbit, you need more engines on it, and that means you're going to need more fuel. by the time you've done all that, with enough extra thrust to carry a payload, what you have is a tanker, that can only get to leo, which is just as well because its poorly optimized for interplanetary - its got way too many engines.

I think you were misunderstanding me. I was not talking about using the proposed SSTO for interplanetary transport. Let me try to explain again:
The full BFR- ITS stack (of booster and ITS) would be overkill for anything but colonization or large scale BEO missions. You rarely need to launch hundreds of tons into a single LEO and that mass to the moon only makes sense if you plan to have a colony there. The ITS in its current configuration really is only good to transport 100 people or the equivalent in cargo (most of it pressurized too) or as a self transporting outpost. If you landed it on the moon, you would have an instant moon village there. But the technology could be adapted to have a launch vehicle with less payload, but less maintenance and a higher launch cadence.
The tanker can launch on its own in its current configuration all the way to orbit, but without any payload. Not even in this configuration would you need to add extra engines for it to work as an SSTO.
But in its configuration as a second stage it is badly optimized to be an SSTO because most of its engines are for vacuum use only. Replace them with engines that are half way between LEO and vac and thus can be used right from takeoff and you have a much more capable LV. The smaller engine bells will probably safe some weight too which would directly translate into more payload. Then add a payload shroud instead of the tanker tank and the result is an extremely cheap (less than 2.4 million per launch), low maintenance SSTO that can have a payload of roughly Falcon 1.1 (or more, some estimates go up to 40 tonnes) to LEO.
For anything beyond LEO, you would probably assemble a dedicated spacecraft in orbit or do on orbit refueling for some mission profiles like to GEO or maybe even to lunar orbit. The point is that you now have options.

okay it looks to me like we are pretty much in agreement. my point was that SSTO is only viable for LEO. which you seem to agree on.

however, as you mention, a transport, in it's current form can only carry itself to LEO - no payload. and that's after modifying its thrusters to high-thrust sea-level optimized, which is going to reduce their isp substantially. (from 382 to 334), thus reducing your total delta-v to 334/382 or about 87%. This is assuming that gives you enough thrust without having to add more engines, thus hurting you delta-v even more. at the end of the day, the transport will NOT be able to reach LEO, even with no payload. the original delta-v was only theoretically -- it was at vacuum pressure and no air resistance.

might be better off starting with a booster and scaling it down (scaling down engines, dry mass, and fuel at the same rate) - except for its lack of heat shield. in any case you still have no payload, which makes the mission moot.

if you want payload, a fully loaded transport (450 ton payload) barely makes it to LEO with the help of a booster.

fully loading it maximizes the return per launch, so you always want to fully load it when you can.

which means you always want to use the booster.

your best option is still two stages.

---

A viable SSTO would need a dramatic improvement in ISP. this means air-breathing engines. Such as SABRE. https://en.wikipedia.org/wiki/SABRE_(rocket_engine) A sabre engine gives you about 10x the ISP in air-breathing mode. That means 10x the delta-v for the same mass ratio.

And bear in mind, once it's out of atmosphere, you don't need high thrust anymore - only enough to reach orbit before reaching the periapsis. (and preferably before the apiopsis). so you can dramatically cut down on the engine mass you need to carry.

Add this to the fact that your rocket engines don't add any more mass at all! They are your jet engines! Now on a two stage it may have made sense to drop you jet engines at this point to save mass. But now they _are_the second stage engines. Your jet engines were never carrying the mass of your rocket engines - they _were_ your rocket engines.

so you got an optimized craft up to the height of where the second stage would normally start (vaccum thrusters, low thrust), without having to drop anything. indeed, all you had to do was carry a little more kerosene (as in like 1/10th the amount you would normally need) (or methane, if you made methalox version), and have a slightly larger tank. That's WAY cheaper than a booster, even a fully reusable one.

but that small cost isn't done being amortized - the air-breathing mode of sabre engines that you had no good reason to drop will come in handy again on re-entry. you can use these to fly to any landing site.

[happyjack27]

How big of a torus style space station could you launch for the 350 ton payload plus whatever you get for scrapping this ship and just using it as a giant booster?

If you can just start putting people in space, never mind on Mars, plenty of people will pay plenty less. Then all we need is Gundanium and Minovsky particles.

what is the minor radius?
out of what materials?
how are you assembling it?

minor radius is going to be limited by the size of the ship carrying the parts, unless:
* you weld them together in space, or something like that
* you use flexible materials or materials that "set" in space (such as concrete)
* you 3d-print it in space
* etc.
in any case we're talking some assembly required if you want a large minor radius.

i wouldn't scrap the ship, i'd reuse it. cost for reentry is low due to aerobraking. cost for making the ship is high. cause to disassemble in space is high. etc. better to just use as a reusable transport.

in any case, at 350 tons a trip, i feel you could build a sizable one in not too many trips.

and while you'd need less than half the space for hydrophonics as you would on mars, due to more sunlight, you wouldn't neccessarily need to reserve any space for hydrophonics - as you could do supply runs from earth.

Any case, yeah, i think it could makes sense. except i'd reuse the ship instead of scrapping it.

add a fuel depot, some storage area, and some docking ports, and you're a stepping stone for mars.

[happyjack27]

How big of a torus style space station could you launch for the 350 ton payload...

as an example, the stanford torus: https://en.wikipedia.org/wiki/Stanford_torus
* mass is estimated at 10 million tons - that includes everything.
* minor radius of 65 meters
* major radius of 895 meters
* assuming 1/3 of the minor radius is usable. that's 2 * pi * 65 / 3 minor length, 2 *pi * 895 major length = ~ 2,296 square kilometers of livable space.

10m tons, at 450 tons a trip, comes out to 22,222 trips.

presumably one'd want to go for something considerably less ambitious...

also i saw it mentioned that bringing materials from the moon instead of earth could dramatically reduce the cost, given that it only has 1/6 the gravity.

it seems to me this depends on where you put it. since leo is further from the moon, and you can't use aerobraking on the moon, round trip from earth to LEO is about 9.4 dv, round trip from the moon is 6.4*2 = 12.8, with a possible aerocapture on earth in one direction that'll save at most 4.1 dv (and probably much less).

if instead it was at a lagrange point - l4 or l5, that's 4.6 dv round trip from the moon, 9.4+4.1*2 dv from the earth, with a max of 4.1 dv saving by aerocaptue (and probably much less). however round-trip earth-to-station trips would require almost twice the deltav.

i think at that point, why not just build the base on the moon, instead of lugging all the stuff out there. i mean, what are you gaining? you're losing in situ resources, natural gravity, lots of time....

either build the station in earth orbit or build a base on the moon, imo.

[zapkitty]

i don't know about you, but i'd go to a toroidal space habitat for 1/50th the price of a mars colony. I think a lot of people would. and i think a lot more people can afford $2,900 than can afford $140,000. you've just turned a life choice into a Caribbean vacation.

... until a single stray ship or chunk of debris evacuates the entire colony biosphere into LEO...

[happyjack27]

i don't know about you, but i'd go to a toroidal space habitat for 1/50th the price of a mars colony. I think a lot of people would. and i think a lot more people can afford $2,900 than can afford $140,000. you've just turned a life choice into a Caribbean vacation.

... until a single stray ship or chunk of debris evacuates the entire colony biosphere into LEO...

one word: LASERS!

[jrvz]

The point was that he wants to send a very large payload (larger than any before) to mars and he only has a perfect launch window every two years (when mars is closest). For operations in earth orbit and even smaller scale missions BEO, an SSTO based on the tanker ITS would be more economic.
...

to get a transport up to orbit, you need more engines on it, and that means you're going to need more fuel. by the time you've done all that, with enough extra thrust to carry a payload, what you have is a tanker, that can only get to leo, which is just as well because its poorly optimized for interplanetary - its got way too many engines.

After spending some time with rocket simulations, I came away with this simple rule of thumb: For an efficient design, the delta V from each stage can't be much higher than the exhaust velocity. LEO orbital speed is roughly double the exhaust velocity using current propellants. So I don't expect a practical SSTO unless we can double the Isp (say, with nuclear thermal propulsion). Yes, you can increase the Isp by getting your oxidizer from the atmosphere - but that only works at comparatively low speed, when you can afford the drag. The primary challenge in getting to orbit is speed, not altitude.

[happyjack27]

i don't know about you, but i'd go to a toroidal space habitat for 1/50th the price of a mars colony. I think a lot of people would. and i think a lot more people can afford $2,900 than can afford $140,000. you've just turned a life choice into a Caribbean vacation.

... until a single stray ship or chunk of debris evacuates the entire colony biosphere into LEO...

one word: LASERS!

seriously, though, me thinks:

* it would be better - more economical and all - to build it one arc-section at a time (at opposite ends of the spoke - so i suppose that's two at a time). you'd build the hub first, then an opposite pair of spokes (which would be habitable, by the way. maybe later to become an elevator shaft with backup ladders or something. then you'd build a pair of arc-sections at a time. the ends are held together with their opposite by tethers, which you'd add or adjust as you added more modules, to keep the whole thing from warping.
* each arc section would be self-contained - it would be a module. so one section is damaged, that only affects that section
* after a couple arc sections, you'd get some redundancy, multiple hab modules, multiple greenhouse modules, etc. so you lose a greenhouse section, you're still good.

so basically i'm saying:

* incremental construction
* modularity
* redundancy

in addition to this, could add an early warning detection system with countermeasures, and put it at a slightly higher orbit or something to get it clear of most space junk.

[happyjack27]

Yes, you can increase the Isp by getting your oxidizer from the atmosphere - but that only works at comparatively low speed, when you can afford the drag. The primary challenge in getting to orbit is speed, not altitude.

i believe i saw on the wikipedia article that the engine is continuously adjustable and thus you can maintain good isp at high altitude and speed.

[kunkmiester]

I posted late and apparently didn't get all the details in there I needed.

I'm looking at an inflatable bigelow style habitat. Diameter and volume aren't as important there as long as you can pack it under a shroud.

This would be a single wheel at a time. If you want a larger single colony they could be bolted together. Not as large as some people think a colony should be but plenty I think.

This would also serve well as a long distance ship.

[happyjack27]

I posted late and apparently didn't get all the details in there I needed.

I'm looking at an inflatable bigelow style habitat. Diameter and volume aren't as important there as long as you can pack it under a shroud.

This would be a single wheel at a time. If you want a larger single colony they could be bolted together. Not as large as some people think a colony should be but plenty I think.

This would also serve well as a long distance ship.

well i just read that the ISS is 450 tons. that's exactly the expected max cargo of the ITS. So... the ISS has a bigelow module on it now, i suppose eye it and scale it.

personally i like the idea of one trip per arc section, a pair of counter-rotating rings, so that you can increase and decrease spin speed for maintenance and expansion and what not. each module would be coated in solar paint for energy (except the greenhouse, which would be made of transparent alumninum (yes, that's a real thing)) and maybe have a superconducting loop for radiation shielding and power storage.

now each section is 450 tons and the dry mass of its transport is 150 tons - so with that you could construct a module with a surface area 3x that of the transport.

lets say each arc section is 6 degrees. then at a full ring, that's 60 sections a ring. and you have 2 rings, so that's 120 sections. that'll take 120 trips, and weight 120*450= 54,000 tons.

at $2,900 per ton launch cost, that's 156M launch cost for full construction - that's roughly the cost of a single transport ship.

seems moderate. big enough to attract tourists but not outlandish.

and one can always add rings.

trying to think of the different modules. so far i got:
storage
hab / dorm
greenhouse
cold storage
workroom
kitchen / dining
recreation/exercise
lab
systems support (life support, energy storage, computing...)
control center / monitoring
Recycling center

Except for different shells between greenhouse and opaque, you have enough room to just make each module a full self-sustaining stack (all rooms). Hell, each one is practically an ISS, except for plenty more volume that's a lot more contiguous. At 10% (12 trips, after building the core), you'd have 3 modules an arm, enough redundancy for it to be habitable, including self-sustaining food, water, and air, via hydroponics and recycling.

[Skipjack]

however, as you mention, a transport, in it's current form can only carry itself to LEO - no payload. and that's after modifying its thrusters to high-thrust sea-level optimized, which is going to reduce their isp substantially. (from 382 to 334), thus reducing your total delta-v to 334/382 or about 87%.

Actually, it would be able to launch to orbit just fine with the current engine configuration (but less fuel). Modifying the engines to be closer to SL would further improve the delta- V, not make it worse. That is because the vac engines are not just dead weight until the air is thin enough for them to work and you can take off with more fuel in the tanks.
The vac Isp of the SL engines is 361 not 334. So you are off there already. Average Isp would be closer to 350.
Delta- v requirement for the typical reference LEO (200 km x 28.5 degrees) is 9300 m/sec, including the average gravity and drag losses.
If we enter the following parameters here:
http://www.strout.net/info/science/delta-v/
Dry mass: 90t
Fuel 2500t
Assumed cargo: 20t
Total spaceship GLOW: 2610t
Average Isp with all engines SL engines: 350
Resulting delta-v: 10842.49
That leaves plenty of margin for the deorbit and landing burns.
So you get an upper class medium lift SSTO RLV with at least 20 t of cargo to LEO.

And then there is still room for optimization here:
1. The smaller SL engines will definitely weight a lot less than the much bigger vacuum engines.
2. You could increase the expansion ratio on some of the engines giving a tad more vac Isp but slightly less thrust. Though some people have indicated that the SL engines may be over expanded for size constraints. One would have to calculate the benefits of that over the flight profile. It might get a few m/sec Isp from that. Though the reduced weight from 1. might gain you more. For SSTOs lightweight structures are generally more important than Isp.
3. You can probably scrap the legs and land in a cradle on the launch pad like they want to do for the booster. That would save at least 5 tonnes (current F9 legs are 2.4 tonnes and this thing is much bigger which would mean much heavier legs).
All this means additional delta-v for more demanding orbits or more payload to LEO.

[happyjack27]

however, as you mention, a transport, in it's current form can only carry itself to LEO - no payload. and that's after modifying its thrusters to high-thrust sea-level optimized, which is going to reduce their isp substantially. (from 382 to 334), thus reducing your total delta-v to 334/382 or about 87%.

Actually, it would be able to launch to orbit just fine with the current engine configuration (but less fuel). Modifying the engines to be closer to SL would further improve the delta- V, not make it worse. That is because the vac engines are not just dead weight until the air is thin enough for them to work and you can take off with more fuel in the tanks.
The vac Isp of the SL engines is 361 not 334. So you are off there already. Average Isp would be closer to 350.
Delta- v requirement for the typical reference LEO (200 km x 28.5 degrees) is 9300 m/sec, including the average gravity and drag losses.
If we enter the following parameters here:
http://www.strout.net/info/science/delta-v/
Dry mass: 90t
Fuel 2500t
Assumed cargo: 20t
Total spaceship GLOW: 2610t
Average Isp with all engines SL engines: 350
Resulting delta-v: 10842.49
That leaves plenty of margin for the deorbit and landing burns.
So you get an upper class medium lift SSTO RLV with at least 20 t of cargo to LEO.

And then there is still room for optimization here:
1. The smaller SL engines will definitely weight a lot less than the much bigger vacuum engines.
2. You could increase the expansion ratio on some of the engines giving a tad more vac Isp but slightly less thrust. Though some people have indicated that the SL engines may be over expanded for size constraints. One would have to calculate the benefits of that over the flight profile. It might get a few m/sec Isp from that. Though the reduced weight from 1. might gain you more. For SSTOs lightweight structures are generally more important than Isp.
3. You can probably scrap the legs and land in a cradle on the launch pad like they want to do for the booster. That would save at least 5 tonnes (current F9 legs are 2.4 tonnes and this thing is much bigger which would mean much heavier legs).
All this means additional delta-v for more demanding orbits or more payload to LEO.

You can't improve delta-v by lowering total fuel. Higher initial fuel means it will eventually reach the point of lower initial fuel, only presumably at a higher altitude and speed.

Let's say with an optimized transport, no booster, you can get 20 tones per launch.

How many launches until that totals 450? That was rhetorical - 23. Compare the cost of 23 such launches to the cost of a single launch with a booster.