Hot answers tagged

72

The quick answer--so they could get the engines back--has already been provided, but I'd like to offer some more historical context to that design decision. Note that the shuttle as originally conceived didn't always drag useless engines into space. In fact, many of the original proposals were developed to be fully reusable, which meant there was no ...


42

So that the reusable engines could be reused. If they were mounted on the expendable external tank, they would have been thrown away each mission.


21

There is a misunderstanding in your question "The engine bell(s) already support the entire compressional stress generated by the weight of the stages above it when the engine is firing..." No, the engine bells do not. (Sutton, 7th edition, Chapter 2.2) The bells mainly withstand the differential pressure forces from the gases flowing through them....


19

I asked one of the copter's engineers, Matt Keennon, what the hole in that one leg's foot was for. He replied that it's only for stowage. ... because of the odd way the copter is held in place under the rover, with all sorts of mechanical constraints from the rover, that one leg could not be held down by a simple lever pressing on the leg strut, so instead ...


14

The answer is a bit more nuanced than Organic Marble presents it. It makes sense to make a force balance to see what bits of engine can take which amount of force. First, let's look at the chamber. It has a static pressure $p_1$ which is balanced everywhere by the walls, except at the throat where there is a large gap. This results in a net force of ...


11

It is important at stage separation to remove as much as possible weight from the upper stage. The interstage weight does not count after separation, but any enhancement of the upper stage engine nozzle does. The interstage weight is small compared to the weight of the upper stages, but it is tiny compared to the weight of the lower stages. Of course the ...


8

An early Martin Marietta Phase A fully reusable space shuttle design proposal, the Spacemaster, had an asymmetrical cockpit layout on its booster component. Note that the "catamaran" booster only has a cockpit in the left fuselage. Never flew of course but it was a serious proposal. Source: Jenkins, Space Shuttle, 1992 edition, page 61


8

Paraphrasing parts of an answer to a different question, hot-staging has a few advantages: It's less complex than staging using ullage motors since fewer parts are involved (whole rocket motors and their plumbing and tanks are missing, as well as the sensors and controllers to make them work correctly). Reduced complexity often means improved reliability. ...


8

This NASA page says that the wheels are: Made of aluminum, with cleats for traction and curved titanium spokes for springy support. The curved part running ~60 degrees along the rim isn't quite in contact with it. It will act as a spring with a hard stop. Having the spring effect in this direction should allow the wheel to remain reasonably aligned even ...


7

Normally the tank is the wall is the structure. This minimizes weight. There are usually cylindrical regions connecting the different propellant tanks - sometimes called "intertanks". This portion of the structure does not contain propellant as the rest does. The shuttle external tank and the Saturn V are examples of that style; I do not know about Falcon ...


7

The original External Tank nose cone design was indeed blunt - almost like a fireplug, as seen in this 1975 concept art. [Image source - lost in the mists of time to me, but NASA somewhere] However, wind tunnel testing at the Arnold Engineering Development Center revealed that this configuration caused unsteady aerodynamic buffeting at some conditions. A ...


7

The largest commercially available width of a roll of stainless steel in the United States is 72 inches. Apparently this is a standard size, and getting something larger would be a custom order, and not quickly and easily available. The vendor Outokumpu (determined by photos of rolls, and the logo found upon them. Very similar to Lucents Brown Ring of ...


6

Colors were decided quite early in the design process by a committee, and were chosen to be consistent between the CM and LM: October 28, 1963. - An LM-CM displays and controls commonality meeting was held at MSC to explore areas in which commonality might be achieved and to provide a plan of action. Areas discussed included principles of layout, switch ...


6

One spacecraft + spacesuits became two spacecraft When the Apollo program started, the assumption was a "direct mode" mission. This plan had no lunar module; there would only be one spacecraft which launched from Earth, landed on the moon, took off, and then returned to Earth. Two contractors with prior experience building aircraft environmental control ...


5

Unfortunateley no direct answer for the Mass Rover, but for space craft overall by using the Rosetta Lander (Philae) as an example: I was listening to a presentation of the Rosetta Lander Mechanical Engineering Team Leader some years ago. He spoke about "dead mass" on the Lander. So as far Philae is concerned. It was not like they have been happy about ...


5

1) Is simple to answer - to get rid of heat. Aluminium has a reflectivity of about 90% in the range below 1000nm wavelength. At a perihelion of 0.2 AU the total power of the Sun is about 30 kW/m² of which maybe 2 kW/m² are absorbed by the sail. A large emissivity helps in getting rid of that. 2) Massive Chromium has an emissivity of about 0.3 in the IR ...


5

With current technology: 4.3AU. From wikipedia, it appears that the most powerful flight-proven RTG had a power density of 5.4W/kg. From NASA, current (as of 2017) solar technology has a power density of 100W/kg. The power output of a solar cell drops off with the square of the distance from the sun. So, let's assume we have 1 kW at 1 AU. The mass of this ...


5

I'll elaborate further on some of the points in other answers and provide some additional background. To put it as simply as possible, a good white spacecraft paint such as AZ93 (ZnO pigment in a silicate binder) is very white in the visible where you eye responds. Also where most of the energy from the sun is located. So the white paint reflects sunlight ...


5

If we count aircraft used as the first stage of a launcher: White Knight Two: Stratolaunch: They may look symmetrical, but they both have a cockpit in one fuselage, while the cockpit space in the other fuselage is empty.


5

The original spy satellites used film cameras. They were pressurized with a half atmosphere of nitrogen. What’s really interesting is that they didn’t need to be, according to the manufacturer. This predates the Mercury program, so I get the sense this was tacked on to the earliest space program to prepare for “Man in Space” The interior of the spacecraft ...


5

Q: Could a rocket's reentry capsule be slowed down by a centrifugal flyweight governor system? A: No! It does not generate external forces or any kind of thrust


5

Provisional launch date 2029 https://millimetron.ru/en/ This project is directly related to the P-2500 (RT-70) radiotelescope at the Suffa radioobservatory. This modification of the RT-70 radio telescope is designed to operate in the millimeter and submillimeter ranges of radio waves. While the radiotelescope is unfinished, there is no point in launching ...


4

The plutonium used in RTGs produces a continuous amount of heat through decay per KG of material regardless of size so can be widely scaled. What does matter is that efficient harvesting of heat energy depends on maximising the difference between the hot and cold sides of the system, so a massive single block would melt everything it touched when built, and ...


4

For the first launch of the ORBCOMM Gen 2 spacecraft there was exactly 1 minute between second engine cut off and second engine restart. Our satellite was deployed during this 1 minute window.


4

There are several conflicting factors influencing aspect ratio, so it’s no surprise that it’s hard to find obvious correlations. A longer, skinnier rocket has less frontal area thus experiences less air resistance. A shorter, fatter rocket has more volume (potential fuel tankage) per surface area (dry structural mass). A larger rocket suffers less from ...


3

This answer helps to explain it--you just accept the boiloff for the short time before the propellant is consumed, and Falcon 9 has to be fueled immediately before launch. But Saiboogu didn't really mention that cryogenic tanks are insulated. That's discussed a bit here in a NASA forum. Delta IV, Space Shuttle external tank, and Ariane V are examples. Cork ...


3

As a counterexample to some statements in the other answers....the actual extreme tip of the shuttle stack was surprisingly sharp.... (personal photo)


3

I'm going to interpret your question as being: "What factors drive the choice between bipropellant and monopropellant thruster systems for spacecraft maneuvering systems?" If that's wrong, advise in a comment, and I'll delete this. This answer is a summary of the paper Performance Evaluation of Spacecraft Propulsion Systems in Relation to Mission Impulse ...


3

Off the top of my head, here are a number of things you would need to address "apart from the electrical specifications". In reality, this is a great case for strong systems engineering in your satellite. Since there will be major tradeoffs between power, pointing, mass, and RF performance/throughput. Materials. This is mostly easy, since by ...


3

Yes, space suit designers exist. For example Final Frontier Design. Also you can see some pictures of their suits, some historic designs and designers themselves at 1, 2 (text in Russian).


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