Hot answers tagged

94

The film gets this mostly right. Merely taking the thrust, and, therefore, the acceleration of the rocket down to zero wouldn't throw the astronauts forward; there are a couple of other effects at work. The first is air resistance; 1st-stage cutoff happens at about 42 mi (68 km) altitude, where there's still some air; this will decelerate the vehicle but ...


80

Because linear increases in delta-v require exponential increases in mass, small changes to the assumptions you make about fuel tank structural mass and engine thrust-to-weight ratio start to make very large changes in the final size of the rocket. For example, if you're getting off a 3.6g planet with a 7-stage rocket, the difference between 88% fuel ...


79

First stages are generally run to depletion (though not complete depletion - I'll get to that later). First stage ascents often use a preprogrammed, open loop guidance system to get out of the atmosphere with a good chunk of downrange velocity. Because winds aloft and other factors may vary, first stage performance also varies somewhat. Upper stage guidance ...


77

There's actually a few outcomes of the second stage that can occur (and some interesting tales to go along with them), but as geoffc has mentioned, second stage reuse is no longer planned for Falcon as Musk thinks the resources to develop it are better spent elsewhere. It's not an insurmountable technical challenge. Intentional Deorbit This is done for ...


76

Methane has the benefit of being easier to store than hydrogen. Mostly passive cooling can suffice to keep it cryogenic, whereas hydrogen needs active cooling, and will still vent over time. Which makes Methane much closer to 'storable' than hydrogen can be. This would make it useful for deep space missions, with long mission durations. Methane is less ...


73

They are used to redirect lightning in the immediate area. This essentially creates a faraday cage, shielding the rocket from being fried by lightning. You can see how high the towers reach, high enough to ensure there is no risk of lightning hitting the craft. Update by @highonrope: The rectangle which the rocket launches through is huge...from the ground ...


69

In addition to the answers that have been given, it should be noted that there is a window of opportunity for a launch to occur, known as a launch window. This certainly occurs when trying to get somewhere such as the International Space Station, but even earth orbiting satellites have a window of time where the rocket can meet its performance. Bottom line ...


67

Your picture is not of a Saturn V, it's of a Saturn IB. The purpose of the elevated platform (known as the "milkstool") is to lift the rocket up so that it can be launched from Pad 39B using the same connections to the launch tower that the much taller Saturn V used. The early Saturn IB launches used the shorter Pad 34 and Pad 37, but by 1973, those launch ...


66

The very first start of a new rocket is a risky endeavour. Since the system is put to test for the very first time as a whole, all kind of things can go wrong and chances are that the rocket doesn't make it into orbit. So a cheap, unimportant payload is needed for the first launch. You don't want to see something worth billions of dollars and having cost ...


64

Your question is based on a false assumption namely: So why didn't NASA take money from the private sector to do these later two on the behalf of corporations? NASA did take money from the private sector to do these things. The STS-5, STS-7, STS-8, STS-41-B, STS-41-D, STS-51-A, STS-51-D, STS-51-G, STS-51-I, STS-61-B, and STS-61-C Space Shuttle ...


62

If you could miniaturize each component uniformly, you're correct that the rocket equation terms would all balance out and the rocket would be capable of the same delta-v performance. However, the impact of atmospheric drag would be much worse; drag force is proportional to cross sectional area, not to volume. A Saturn V loses less than 1% of its delta v ...


61

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 ...


60

The Apollo Lunar Module has launched from six lunar sites: Apollo 11 — Mare Tranquillitatis Apollo 12 — Oceanus Procellarum Apollo 14 — Fra Mauro Apollo 15 — Hadley/Apennines Apollo 16 — Descartes Apollo 17 — Taurus-Littrow


58

First of all, a typical launch window for going towards Mars is about 2.5 hours maximum. As a goal is to send the payload towards Mars, that is one limit to the window. Also, there are a number of other factors affecting a launch. These include: Availability of the range Personnel that are required. A lot of people are required on launch day from quite ...


56

A big difference is that you wouldn't need to leave someone in lunar orbit. We now have experience and confidence in the remote operation of an uncrewed vehicle. So you could have a crew of two instead of three. Or perhaps a crew of three to the surface with a larger LM. Overall, there would be much more automation, especially for the landing process, ...


55

T minus zero appears to generally indicate the moment of booster liftoff, but can also indicate something different. To borrow Cort Ammon's wording, it's an action or event that results in a substantial change in the amount of control you have over the situation. Taking the countdown for the Falcon 9 as an example, T-00:00:00 is the instant of lift-off; in ...


52

The Delta V requirement to launch is about 14 km/s to low lunar orbit, per Wikipedia. That means that you would have to achieve a speed of 14 km/s in order to orbit the moon. Some of that will need to be done from space, but most of it could theoretically be achieved from the ground. So, what do you need to do to make that happen? In World War II, the ...


52

Those are jets of water released by the sound suppression systems installed on the pads and the mobile launcher platforms to protect orbiters and their payloads from being damaged by acoustical energy, reflected from the platform during the liftoff stage of a rocket launch. For example, this is the sound suppression system at the NASA Kennedy Space Center's ...


52

SpaceX regularly includes a timeline of noteworthy mission events in their live streams. One of the founding principals of SpaceX was a desire to inspire humanity to be excited about space travel again. Educating and explaining as you demonstrate is one good way to get people more engaged and interested. I also get a strong impression that Elon Musk and ...


50

Why not deliver something useful to the space station like a new living segment? Many, many reasons. A dummy payload is almost always used on the maiden flight of a new rocket. The risk of failure is too high to send anything of value as a payload. SpaceX cannot send something to the ISS just because they want to do so. They can only deliver cargo to the ...


50

The rocket is autonomous, it flies itself. The navigational math, engine, and flight dynamics of a Earth-based orbital class rocket in operation are far too complex for manual operation, especially remote manual operation. Even simpler rockets (like Apollo LEM) that could be flown manually have still attempted to offer automatic operation in the interests ...


49

The original design called for say 500,000lbs of thrust. After years of development, tweaks, changes in the real world (bonuses, like the pressure of the fuel in the line from the entire length of the tank boosts performance (SLS has a sort of issue with this)) means the production engine actually produces 540,000lbs of thrust. Thus full power is now 108%. ...


49

Hobbes has already showed you a diagram of the Falcon 9 launch profile, so I won't repeat that. Note: This answer is not intended to be a complete, scientific treatment of the subject. I knowingly and deliberately simplify, gloss over and ignore things in several places, in order to explain this in a way that hopefully makes sense to the OP while still ...


48

LF2/LH2, or liquid difluoride liquid dihydrogen bipropellant (binary cryogenic fuel) has a specific impulse of 410 seconds (by weight) at sea level, which is more than e.g. LOX/LH2 (liquid oxygen liquid dihydrogen) with average specific impulse by weight of 391 seconds, also at sea level. As the oxidizer is in both cases on board and one of the binary ...


48

This post highlights some misconceptions, so let's do this with big letters. Launch is about going fast, not high A helium balloon will get you to the edge of space. It takes a large and expensive rocket to get into orbit. Ok, one at least 20 m long. Very very fast "But the plane can give you 600 mph" you say. Well, that's nice, we have 268 m/s of the ...


48

It isn't really feasible to launch your own rocket, unless you have a lot of money to spend. The required power is immense. Hitting sub-orbital might be possible, and has been done once by amateurs, but they received sponsorships and had a team dedicated to making it happen. The trick to an orbital rocket is not just to get high, but also fast. The speed ...


46

Trajectory of the Falcon 9 first stage: Graphic courtesy ZLSA Design (zlsa.github.io) As you can see, before the boostback burn, the stage flips so the engines point in the direction of travel. When the engines fire, this slows down the stage. This trajectory is used when the stage returns to the launch site (and for some early experiments where the ASDS ...


46

That's a mistranscription of OMS Burn, or Orbital Maneuvering System burn. The OMS system is how the shuttle changed its orbital characteristics. You can read about it here. One, two or more might have been used to fine tune the orbit, avoid space debris, rendezvous with the space station, etc.


45

Not even close. In fact, at 12 seconds in, you're looking at maximum damage to not just the pad itself, but the surrounding area as well. You're going to have tons of debris (most of it burning and possibly carrying even more unburnt fuel) fall from 1500-2000ft range in a giant umbrella of destruction. In 1997, a Delta II carrying the GPS IIR-1 satellite ...


43

Methane (CH4) and RP-1 are roughly equivalent in realizable performance. As previously mentioned by other posters, CH4 has slightly higher impulse – about 370 s in vacuum vs the 360 s – at the same chamber pressure of 7 MPa. But, this is counterbalanced by its lower bulk density of about 830 kg/m3 vs about 1030 kg/m3. Bulk Density is the density of the ...


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