63

Up until this flight of Falcon Heavy, officially, SpaceX could not fully deliver a satellite to [nearly circular] GEO (Geosynchronous Earth Orbit), but only to a [highly elliptical] GTO (Geosync Transfer Orbit) that expects the payload to circularize its own orbit once at the appropriate altitude. This consumes fuel, and fuel for station keeping is one of ...


43

There are some major challenges with this. For starters, the engines of the first stage produce far too much thrust for the last stage, which would require extra structural mass to allow the rocket to hold together, and would not allow manned rockets at all, as humans have fairly tight g-force limits. If you reduce thrust to manage these problems, you're ...


30

The J-2 engine used on the second and third stages of the Saturn V has a "PU valve" (propellant utilization) on the oxidizer turbopump. Adjusting the mixture ratio with this valve primarily provides a mechanism to ensure that the hydrogen and oxygen propellants are depleted at the same time. Secondarily, it allows a tradeoff between specific ...


27

That's from within the propellants tanks of the upper stage after Dragon separation and the microgravity environment saying hello. Lack of acceleration (stage engine is shut off during separation) acting on propellants when looking at them from inertial frame of reference (the tank itself) means they're essentially in free-fall together with the stage ...


25

The second stage performed an engine relight test and re-entered over the Indian Ocean about an hour after launch. Below is the reentry region defined by a NOTAM (Notice to Airmen). Relighting the second stage is an important step in launching satellites to geostationary orbit, so their successful test is promising.


23

Nathan's answer is good and cover almost everything but let me add a last bit: An engine nozzle can be optimized for only one given altitude ambient pressure. This has a great impact on the rocket performance. You probably wouldn't want to drag that heavy, inefficient engine all the way up, even if you could. Some designs attempt to circumvent this issue ...


21

The Merlin engine used by the Falcon 9 burns a fuel-rich RP-1/LOX mixture, like most other rocket engines. That means the exhaust coming from the engine contains unburnt fuel, mostly in the form of soot. You can see that in your picture: There is a dark exhaust. At sea level the excess fuel/soot burns off with atmospheric oxygen, leaving a flame trail ...


20

The From the annotated Apollo 8 Flight Journal, in the notes after the 2:36 mark, we see that the interstage separation happens well after the J-2 engines on the second stage are running: If, at staging, the interstage were to stay with the S-IC, there is a danger that any slight rotation of the massive first stage would cause contact between it and the ...


20

If the failure of the S-IVB third stage didn't significantly damage the Command/Service Module, and the CSM was able to separate from the S-IVB, then this is a surprisingly benign failure mode and the crew would be likely to return to Earth safely. Firstly, note that at all times during the TLI burn, the spacecraft trajectory is an elliptical orbit with ...


18

Agena is a much smaller and less powerful stage than Centaur. Astronautix gives Agena-D a loaded mass of about 6.8 tons, as compared with around 23 tons for Centaur (though this varies quite a bit with version changes). Centaur uses the RL10 hydrogen-oxygen engine, with specific impulse up in the 440-450 s range depending on version, but Agena used UDMH ...


18

I found a nice article about the evolution of the IUS in this issue of the Crosslink newsletter. Originally, NASA intended to develop a reusable "space tug" that could deliver satellites from the relatively low orbits reachable by STS to geosynchronous and other high orbits. This was a big concept that was going to take years to develop, so NASA ...


17

The burning seems to be after the 5 J-2 engines on the second stage fire. Each J-2 has about 230KLbs of thrust for well over a million lbs of thrust aggregate. ANYTHING exposed to 1 million lbs of LOX/LH thrust is very likely to burn. No doubt they ran some oxygen and hydrogen through the engines to pre-cool them before igniting, (like the SSME does, like ...


16

The mass required to deliver the required $\Delta\mathrm{V}$ depends on the Isp and the dry mass ratio of the stage. It does not depend on the thrust, except to the extent that a high thrust would increase the mass required due to a large engine and feeds. For a given Isp, the thrust just determines how long it takes to use all the propellant. For an ...


15

The payload penalty to recover the second stage turned out to be more than they initially expected, and as such, SpaceX has given up on second stage recovery for the Falcon 9 booster. The problem is, the first stage is only 160K up, Mach 5 or so which is very fast and high, but the second stage is basically orbital, which is much higher (maybe) and faster. ...


12

Any sensible answer to your question should make an implicit assumption on the number of engines to be ordered overall. That is, we need to know the number of planned manned flights to Mars and other important destinations, since fixed (sunk) costs of an NTR-based program are significant. The following ideas are based on a few NASA documents discussing NTRs. ...


11

While TildalWave's answer is mostly correct, he missed one important thing. This is not the RP-1 fuel, it's Liquid Oxygen, the oxidizer - floating in microgravity after the Merlin 1D Vacuum engine shutoff. There are two very clear giveaways for this. RP-1 has a yellowish hue, whereas Liquid Oxygen has a more characteristic blue color, which can be seen in ...


11

When this was captured, it was at the end of the rocket flight. Looking carefully at this, I don't see any other similar nozzles. Furthermore, I didn't see any evidence of this being used in flight. I'm going to assume from all of this that it must be the vent value for the LOX, which was mentioned in the video recording immediately before. What happens ...


11

PSLV is a bit of a weird duck because it's a transitional step from small solid-rocket designs to larger ones that rely more heavily on liquid rocket engines with higher specific impulse. It doesn't represent an uncompromised "clean sheet" optimal design. ISRO's first two orbital launcher designs, SLV (1979-1983) and ASLV (1987-1994), were small, not-very-...


11

According to tweets from Elon, at least part of the decision is due to their design for dealing with the reentry heat: instead of adding ablators to cool the craft on reentry, Starship is going to actively cool the hot side with liquid methane. Steel is better at coping with this than carbon fiber. Tweet 1: Usable strength/weight of full hard stainless ...


10

In the past 6 years NASA and the DOE have put a fair amount of effort into estimating the cost to recapture NTP technology assuming either graphite based or tungsten CERMET fuel. The estimates to include fuel development, reactor development, reactor testing and infrastructure ranged from $4 to 6 billion over 10 to 15 years. However, where there has been ...


10

It's hard to see in your picture but there are actually two big pointy things on the Transtage. They are propellant tanks. The one in your picture is the nitrogen tetroxide tank. Reference More recent stages do, of course, have propellant tanks, but they usually don't hang down below the stage structure in such an undignified fashion. Perhaps because ...


9

Starting with this list of missions to Mars, I first looked at the launchers used. The Proton-K, Ariane 5 and Titan 3 Centaur are the heaviest in the list. That eliminates most candidates. I initially expected Curiosity to lead at 3893 kg. But the Russians have launched some heavier probes, e.g. Mars 3 at 4650 kg for the orbiter plus lander. The Mars 96 ...


9

Since Centaur Upper Stage has a long flight history*, and it did experience hydrogen-venting problems in its early versions resulting in several modifications to its pressurization system, I was fairly certain that it ought to have several relief valves in place; From CENTAUR D-1T PROPULSION AND PROPELLANT SYSTEMS, William E, Goette, Lewis Research Center, ...


9

You haven't defined "optimal" here. The commercial launch business is more concerned with cost optimization than mass optimization. Atlas V offers two variants of Centaur, with one or two RL10 engines on it, although the two-engine version hasn't yet been flown on an Atlas V; adding solid rocket boosters seems to be incrementally more cost-effective than ...


9

"Kick stage" or "apogee kick motor" is a loosely defined term for the last stage of a satellite launcher. Frequently it's the stage that puts the satellite into its final orbit. The term is not specific to RocketLabs. It might be developed independently of the rest of the launcher; for example a given launcher might be able to launch large payloads directly ...


8

Is it normal for thrusters to “ice up”? The thing circled in your photo is a LOX vent, not a thruster. The puffy white object is solid oxygen. Your question is directly answered at T+1.05:25 in the Iridium-6/GRACE-FO webcast: Currently you can see the camera on Stage 2, looking at the upper stage engine, that white object you see is solid oxygen, very ...


8

No. Currently operating launchers using other fuels for their upper stages include Falcon 9 (RP-1), Soyuz (RG-1 for the 2nd stage, UDMH/N2O4 for the Fregat upper stage), Vega (solid fuels for 2nd and 3rd stages, UDMH/N2O4 for the AVUM 4th stage), and Electron (RP-1).


8

The typical lifetime of an upper stage rocket body (in GTO) varies from few weeks to few decades. This large variation is due to the sensitivity of the orbital evolution to the initial launch conditions, atmospheric density variations, etc (http://adsabs.harvard.edu/abs/2004AdSpR..34.1227S). https://aerospace.org/reentries has a nice database of launch ...


7

It's a stabilization technique. I'm not sure what you mean by "is it necessary"...they don't do things "just because" in rocketry. It's an alternative to three-axis stabilization. The satellites are usually despun after the burn(s), often by the amusingly named "yo-yo de-spin". (good animation at link)


7

For an upper stage, look to the Long March rocket series as a case history. For Long March 2-4, the boosters use hypergolic fuels while the upper stage burns LOX/LH2. Given that they have decades of experience with the hypergolic engines, that suggests LH2 is cheaper. Essentially they made the decision between building a bigger booster or adding strap-ons or ...


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