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SpaceX Discussion Thread

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9 minutes ago, XB-70A said:

According to Spaceflightnow.com

Cape Canaveral could see two launches in one day Thursday

 

Two others websites I'm looking at are even more optimistic as they already have put the 30W-6 launch as confirmed for March 1st.

Man, it's like the 60's all over again in here! :D

On a completely different note, how early do you all think a reusable booster like F9 could have been built, technologically speaking? Good enough engines were available as early as the 70's in the USSR, but limitations on computing technology would have probably prevented it until at least the early 90's. Any thoughts?

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DC-X was flying in the early 90s. I think it could have been done earlier.

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15 minutes ago, tater said:

DC-X was flying in the early 90s. I think it could have been done earlier.

Yes, you need an restartable engine and control systems who are good enough. 
Turnaround reentry and landing. 

However I think it could be done during the 70s, it would be far more expensive to develop back then. 
Hard to change an existing rocket too so you needed an new design. 

Edited by magnemoe

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8 minutes ago, magnemoe said:

Yes, you need an restartable engine and control systems who are good enough. 
Turnaround reentry and landing. 

However I think it could be done during the 70s, it would be far more expensive to develop back then. 
Hard to change an existing rocket too so you needed an new design. 

Could it, though? Computing technology in the 70's was sufficient to run the UPFG guidance algorithm used on the Shuttle, but whatever SpaceX uses is almost certainly far more sophisticated than that. We don't know much about the SpaceX guidance algorithm, but I think it's safe to say running it on 70's computing hardware would be a stretch. There's another consideration, too - GPS. ASDS landings are entirely dependent on GPS technology for location-finding, and doing it by dead reckoning is not reasonably possible. The problem is, the GPS network only reached full operational capability in 1990, and precision GPS was only made available to the public in late 2000, which makes even the 90's problematic. Of course, RTLS isn't quite as dependent on GPS...

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1 hour ago, sevenperforce said:

Not possible. The interstage is black because it is unpainted carbon fiber; the core is painted aluminum. Ya gotta paint the aluminum but carbon fiber is good on its own.

Besides, if it were all black someone might mistake it for an Electron. -_-

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1 hour ago, sevenperforce said:

The core is painted white to help keep the subcooled LOX and RP-1 cool. Black paint would cause solar heating.

They should paint it silver. Because it may reflect more light, but mostly because it would be much more awesome to see a silver rocket

46 minutes ago, IncongruousGoat said:

Man, it's like the 60's all over again in here! :D

On a completely different note, how early do you all think a reusable booster like F9 could have been built, technologically speaking? Good enough engines were available as early as the 70's in the USSR, but limitations on computing technology would have probably prevented it until at least the early 90's. Any thoughts?

well baring in mind the lack of OH&S back then you could just put a pilot on the booster. Doesn't have to go to space, so capsule can be relatively light. Mass penalty is less because its a bottom stage. Yeah I'm not serious, but it would be possible.

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25 minutes ago, Antstar said:

They should paint it silver. Because it may reflect more light, but mostly because it would be much more awesome to see a silver rocket

That would probably cost more.

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9 minutes ago, sevenperforce said:

That would probably cost more.

For sure. And I don't think it would like reentry heat much. But it would still LOOK awesome :D

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1 hour ago, Antstar said:

They should paint it silver. Because it may reflect more light, but mostly because it would be much more awesome to see a silver rocket

They should paint it pink.

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1 hour ago, Antstar said:

They should paint it silver. Because it may reflect more light, but mostly because it would be much more awesome to see a silver rocket

1 hour ago, IncongruousGoat said:

Most silver surfaces actually absorb more light (especially at infrared and ultraviolet ranges) than titanium white. It's just that what they do reject, they reflect rather than scattering.

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ICBM reached ~200 m accuracy in 1980s, ~500 m in 1970s.
Board computer of Apollo LEM had enough programs to perform any phase of flight automatically.
Cruise missiles of early 1980s had accuracy ~5..15 m and enough calculation power to fly at 50 m altitude with 6 areas of positioning on the route. (Taking into account the atmosphere).

So, I guess that rockets could return and land in late 1970s..early 1980s if they wanted.
Just maybe not so accurately, on a landing pad ~500 m wide. But unlikely somebody could imagine that they have to land on a barge rather than on land.

Also let's remember the WWII German anti-aircraft reusable missile which should return and land if had missed. (Can't recall its name)

Edited by kerbiloid

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1 hour ago, IncongruousGoat said:

Could it, though? Computing technology in the 70's was sufficient to run the UPFG guidance algorithm used on the Shuttle, but whatever SpaceX uses is almost certainly far more sophisticated than that. We don't know much about the SpaceX guidance algorithm, but I think it's safe to say running it on 70's computing hardware would be a stretch. There's another consideration, too - GPS. ASDS landings are entirely dependent on GPS technology for location-finding, and doing it by dead reckoning is not reasonably possible. The problem is, the GPS network only reached full operational capability in 1990, and precision GPS was only made available to the public in late 2000, which makes even the 90's problematic. Of course, RTLS isn't quite as dependent on GPS...

I can't imagine that the space communication network wouldn't be sufficient for finding your location in space, and it would only take 3 or so base stations to establish location for landing (I'd recommend at least 6,  3 for course location far away and 3 for fine location up close.  Presumably using a switchover during the "dead time" during re-entry when the plasma blocks radio signals.

I'm fond of the early shuttle plans that included both "booster" shuttles (get up to mach 9 or so and then landed by pilots) and "orbiter" mini shuttles.  Of course this doesn't work as well if you insist on a "payload bay" that can return satellites to Earth (your orbiter grows to the size of the real shuttle orbiter).  A better question is to ask why the shuttle's maiden launch needed astronauts aboard if the 1970s algorithms (and hardware) were that great (it was the only manned maiden launch, and considering just how many cutting edge tech (by rocket industry standards) I'm sure that decision was unpopular at NASA).

4 minutes ago, kerbiloid said:

Also let's remember the WWII German anti-aircraft reusable missile which should return and land if had missed. (Can't recall its name)

In "Rockets and People" there was a mention of a design of a Soviet "rocket plane" designed as an interceptor.  It was meant to be manned, but I don't recall it ever being deployed in battle.  It was designed with a similar philosophy as the de Havilland DH.98 Mosquito in that it was made of wood, made by cabinetmakers (who otherwise would be simply called to the front), and went one step further and used a rocket engine instead of extremely valuable aircraft piston engines (presumably the rocket engines required different machine tools).

Edited by wumpus

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30 minutes ago, softweir said:

Most silver surfaces actually absorb more light (especially at infrared and ultraviolet ranges) than titanium white. It's just that what they do reject, they reflect rather than scattering.

Yes, I know. But if we are being litteral and serious, then metallic gold, please. I believe that is the best performing across the full solar emission spectrum. And a gold rocket would look nice too

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1 hour ago, IncongruousGoat said:

Could it, though? Computing technology in the 70's was sufficient to run the UPFG guidance algorithm used on the Shuttle, but whatever SpaceX uses is almost certainly far more sophisticated than that. We don't know much about the SpaceX guidance algorithm, but I think it's safe to say running it on 70's computing hardware would be a stretch. There's another consideration, too - GPS. ASDS landings are entirely dependent on GPS technology for location-finding, and doing it by dead reckoning is not reasonably possible. The problem is, the GPS network only reached full operational capability in 1990, and precision GPS was only made available to the public in late 2000, which makes even the 90's problematic. Of course, RTLS isn't quite as dependent on GPS...

You can do with multiple radio signals for accurate positioning. You can do more remote, exception is a gap during reentry and probably final landing burn. 
You do not need to space harden the computer, it can also be larger or you use multiple specialized for its task like going analogue for the landing, they could soft land probes on Moon after all. 
Forget the slam dunk you would need engines for landing, one tricks might be to use smaller engines for gimballing like Soyuz does, have them also work as landing engines. 
Do it mechjeb style, burn to stop 300 meter above ground, then do an soft landing, yes you suffer in dry mass and landing efficiency. 
Main issue is more about thinking outside the box. 

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2 minutes ago, wumpus said:

I can't imagine that the space communication network wouldn't be sufficient for finding your location in space, and it would only take 3 or so base stations to establish location for landing (I'd recommend at least 6,  3 for course location far away and 3 for fine location up close.  Presumably using a switchover during the "dead time" during re-entry when the plasma blocks radio signals.

I'm fond of the early shuttle plans that included both "booster" shuttles (get up to mach 9 or so and then landed by pilots) and "orbiter" mini shuttles.  Of course this doesn't work as well if you insist on a "payload bay" that can return satellites to Earth (your orbiter grows to the size of the real shuttle orbiter).  A better question is to ask why the shuttle's maiden launch needed astronauts aboard if the 1970s algorithms (and hardware) were that great (it was the only manned maiden launch, and considering just how many cutting edge tech (by rocket industry standards) I'm sure that decision was unpopular at NASA).

I had no idea this was seriously contemplated (I know the shuttle design was originally much smaller). Were the boosters more like rocket or jet?

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3 minutes ago, Antstar said:

I had no idea this was seriously contemplated (I know the shuttle design was originally much smaller). Were the boosters more like rocket or jet?

Hopefully rocket.  You want to get the thing to roughly mach 9, and jets are extremely difficult to get to mach 3.  In general you want to split your delta-v into even sections (it doesn't always work that way, but it is great place to start).  Of course, using jets would probably get discarded earlier (although I really hope the X-43 program is still funded somehow.  It really looks like it was getting the ability to get significant delta-v out of an airbreather stage).

The more I learn about *all* the requirements the shuttle had to fulfill, the more impressed I am with the final design.  There are a lot of ways to improve the shuttle (for what it eventually did), but they all generally won't meet the requirements Congress and NASA set forth.  All of the issues with the design can be laid at those who came up with those broken requirements.

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I think we probably had good enough computer targeting to do decent hoverslams, but I don't know that we had first-stage engines capable of reliable air starts.

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4 minutes ago, sevenperforce said:

I think we probably had good enough computer targeting to do decent hoverslams, but I don't know that we had first-stage engines capable of reliable air starts.

This had to be developed and tested, don't think it was an part of the merlin design specifications either. Again you can use special landing engines but you probably want to use the mains for braking. 

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1 hour ago, Antstar said:

I had no idea this was seriously contemplated (I know the shuttle design was originally much smaller). Were the boosters more like rocket or jet?

NARshuttle1970.jpg

Horizontal takeoff under jet propulsion and relatively modest climb, then fire up the rockets and pitch up hard. Both vehicles use jet engines to RTLS and land on a runway. 

The shuttle was supposed to carry (among other things) drop-in fuel tanks for a reusable moon transfer tug.

4 minutes ago, magnemoe said:

This had to be developed and tested, don't think it was an part of the merlin design specifications either. Again you can use special landing engines but you probably want to use the mains for braking. 

That's the point -- you can't use your main engines for braking unless you can reliably air-start them while flying tail-first. Supersonic retropropulsion was completely pioneered by SpaceX.

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46 minutes ago, wumpus said:

Hopefully rocket.  You want to get the thing to roughly mach 9, and jets are extremely difficult to get to mach 3.  In general you want to split your delta-v into even sections (it doesn't always work that way, but it is great place to start).  Of course, using jets would probably get discarded earlier (although I really hope the X-43 program is still funded somehow.  It really looks like it was getting the ability to get significant delta-v out of an airbreather stage).

The more I learn about *all* the requirements the shuttle had to fulfill, the more impressed I am with the final design.  There are a lot of ways to improve the shuttle (for what it eventually did), but they all generally won't meet the requirements Congress and NASA set forth.  All of the issues with the design can be laid at those who came up with those broken requirements.

Yeah, if you haven't seen a movie called pentagon wars, you should. And its not like the military learned from this ability to be a jack of all trades and master of none https://en.wikipedia.org/wiki/Joint_Strike_Fighter_program

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1 hour ago, wumpus said:

Presumably using a switchover during the "dead time" during re-entry when the plasma blocks radio signals.

If your craft is big enough, you can use radio during reentry - just coming from above.

Terminal active radio guidance is something the Pershing MARV had.

58 minutes ago, Antstar said:

I had no idea this was seriously contemplated (I know the shuttle design was originally much smaller). Were the boosters more like rocket or jet?

Hypersonic jet.

spiral43.jpg

1 hour ago, wumpus said:

In "Rockets and People" there was a mention of a design of a Soviet "rocket plane" designed as an interceptor.  It was meant to be manned, but I don't recall it ever being deployed in battle.  It was designed with a similar philosophy as the de Havilland DH.98 Mosquito in that it was made of wood, made by cabinetmakers (who otherwise would be simply called to the front), and went one step further and used a rocket engine instead of extremely valuable aircraft piston engines (presumably the rocket engines required different machine tools).

That's basically the Me-163 - or, if we dig into the Soviet files, the Bereznyak-Isaev BI-1, preceded by several of Korolev's rocket gliders. Nitric acid oxidizer, pretty advanced for its age, and it was starting ground tests by the time of Operation Barbarossa.

bi1popkol.JPG

Wooden aircraft were nothing unusual back then, though.

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The Grumman concept:

NASM-A19740732000_PS01.jpg?itok=6OC_0fpA

Vertical takeoff on rockets; horizontal landing on jets. The orbiter carries two crossfed drop tanks discarded at 300 m/s under orbital insertion. 

3 minutes ago, DDE said:

That's basically the Me-163 - or, if we dig into the Soviet files, the Bereznyak-Isaev BI-1, preceded by several of Korolev's rocket gliders. Nitric acid oxidizer, pretty advanced for its age, and it was starting ground tests by the time of Operation Barbarossa.

bi1popkol.JPG

Wooden aircraft were nothing unusual back then, though.

On the subject of rocketplanes, let's not forget the German interceptors which launched under hypergolic rocket power and then had to glide back.

They were too fast to actually shoot at Allied bombers, so they came with vertically-oriented rockets in the wings. The rockets were activated using a photosensor, so the pilot merely had to arm a pair of rockets, steer underneath an Allied bomber, and the shadow of the bomber above would trigger the rockets and fire.

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