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35

Between them, Spirit and Opportunity spent the equivalent of 22 years performing geology fieldwork on Mars. In that time, they managed a scientific output comparable to what a single geology grad student could do in two weeks. Between them, Luna 16, Luna 20, Luna 24, and Chang'e 5 returned about 2.3 kg of material from four sampling sites. Neil Armstrong, ...


32

One of the most important reasons is that robots don't make great interview partners. A significant part of space missions is outreach and inspiring people. Another important part is giving people a different view of our planet. Astronauts over and over again describe the awesome feeling of being able to see how small and fragile our planet is, and the ...


22

At least for some vehicles, "dynamic pressure is closely monitored" is not correct. You need to have an air data probe to actually monitor it, and not all vehicles do. Shuttle: Dynamic pressure was not actually measured1 during ascent so "Max Q" was not either. The magnitude and time of Max Q was predicted by prelaunch simulations, and ...


10

The Falcon 9 burns somewhere around \$200k-300k in propellant (stated to be \$200k in 2015, but the vehicle's grown in size since then). For non-expendable launches, it puts about 16000 kg into orbit, so that's about \$20/kg. Starship burns cheaper methane fuel, and propellant cost is estimated at about \$500k/launch when purchased in volume. Total payload ...


9

What is the theoretical fuel cost to launch 1 kg of payload to orbit on an ideal rocket (rocket with 0 kg dry mass)? We can use the rocket equation to get a rough idea of the fuel required. $$\delta V = v_e ln \frac{m_0}{m_f}$$ $\delta V$ required to reach LEO is 9.4 km/s $v_e$ is the exhaust velocity of the rocket, 3 km/s is pretty good for a chemical ...


7

Why is the physical presence of people in spacecraft still necessary? Because robotics and AI aren't so developed as to totally replace humans (who are very versatile). Having said that, there are lots of robotic space probes and landers, but not too many people in space.


7

Colloid microthrusters are probably the smallest. If you want liquid, I'd say RD-4D RCS thruster used on Apollo spacecraft, at 8lb weight would be a reasonable example.


7

The MR-106E rocket engine is most likely the smallest liquid rocket engine. It uses hydrazine monopropellant. It could easily be held with one hand. It has a length of 18 cm, and weighs about 1 pound (about 500 grams). It was used on NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite.


6

Partial answer because based on a simulation doesn't address the secondary question about changes with throttling The paper CFD SIMULATION OF A LIQUID ROCKET PROPELLANT (LH2 /LOx) COMBUSTION CHAMBER shows a "flame front" in the sense that majority of the combustion reactions take place in a relatively small area of the combustion chamber. (zero ...


6

There are ways to measure dynamic pressure, and in aerodynamically complicated spacecraft (like the shuttle) if measured on its three four "nosecones" it could conceivably occur at (at least somewhat) different times in different places. And yet when we watch a launch there is a specific time when the announcer calls out "Max-Q!" at which ...


6

Necessity Why is anything "necessary"? Who gets to define that? The biological imperative, if you will, is to survive, reproduce, and exploit every niche. Look all over the planet, and you will see that living systems have done exactly that, to a degree well beyond human engineering. If space is a new niche for humans, especially other planets, ...


5

Why is the physical presence of people in spacecraft still necessary? The physical presence of people on most spacecraft is not necessary, not even those rated to carry passengers. Having humans doing the exploring in person is mostly aspirational rather than actual; most space exploration has been done remotely, using probes of varying complexity and ...


5

Sure. Take a look at a 1960s Mercury-Atlas vernier thruster: Probably not something you can hold comfortably with one hand, but going by the scale of the stepper motors, definitely carryable with two hands.


5

Longest Static Fire of a rocket engine: With you showing interest in the SSME firing (which was probably not attached to a full stage), the Glen Research Center operated a xenon gas engine (0.236 N thrust) continuously from 2003 to 2009 (48,000 hours or 5.5 years). Longest Static Fire of a complete solid-fuel stage: (See other answer for longest liquid-fuel ...


5

According to the Flight Manual, the Saturn V upper stage LOX tanks were maintained at 38-41 psi (2.6-2.8 bar). The first-stage LOX tanks were kept at lower pressure, 20-24 psi (1.4-1.7 bar). It appears those values may have varied slightly on different flights.


4

The ullage in the space shuttle external tank liquid oxygen tank was pressurized by ground-supplied helium to its flight pressure level of 20-22 psig (1.4 - 1.5 bar) at 2 minutes and 55 seconds before liftoff. Before that its vent/relief valve was open and the tank was approximately at ambient pressure. After liftoff ullage pressure was maintained at the ...


4

The success rate of the Saturn V is attributed, among other factors, to the extensive testing, in particular testing beyond the design parameters. The three stages of the Saturn V had the nominal thrust durations: S-1C: 160-170 seconds S-II: 360-370 seconds S-IVB: 450-500 second (combined) All stages were subjected to full-duration static firing tests, ...


4

Of course there are the RCS (Reaction Control System) engines used in every manned space ship as well as in larger satellites and space probes like Voyager, Cassini-Huygens and New Horizon. Small cubesats don't use them. See the red markings in the drawing of the Apollo CM and the LM image of Apollo 11.


4

Even if robots were still used for most of the fieldwork (which I think is likely even with a human presence because spacesuits, and the humans inside them, are fragile and expensive), having a human in a habitat nearby would be a great advantage for scientific research. Due to communication delays and often the lack of a stable radio connection, near real-...


4

Rocket Labs Electron rocket is made of carbon fibre, this gives them the black color you describe. It is not painted black deliberately, in fact they do not paint it at all to save weight. The Falcon 9 is painted white partly to preserve the aluminium structure, partly to increase its albedo. However SpaceX have stated that the thermal effects are so minimal ...


4

Foreword: This is generally considered a difficult proposition, and books have been written on the subject. This "technology" could also fall under ITAR, so that's why there was some hesitation in answering your question at first. The consensus in the model rocket community seems to be as long as the goal is straight up, and not towards a target, ...


4

Rocketlab's sea level Rutherford engine is probably near the upper limit. It masses 35kg, and estimating from the 25cm nozzle diameter is about 75cm high. Despite it's awkward shape, that would still be single hand lift-able by a person of average/somewhat above average strength. (Originally from Rocketlab)


3

Speed of light For Mars, at its closest point it takes 3m 22s to get a signal one way. We would need another 3m 22s to see what's happened. At its furthest we're looking at 24m each way. So good remote control is basically impossible. We don't have good AI yet, so we only have three options for craft we send out into space. They can be pretty dumb and just ...


3

The "X by Y" orbit convention is perigee and apogee altitude above some surface reference level, not the semi-major and semi-minor axes. "114 by 116 miles" means the low point of the orbit is 114 miles above the surface, and the high point is 116 miles above the surface. You can add the appropriate Earth radius figure -- about 6378 km for ...


2

If we enlarge a big rocket by a scale factor of two for all diameters and heights what will happen? All area will increase by a factor of four and all volumes and weights increase by a factor of eight. For eight times the mass we need eight times the thrust. But if we take the same reliable rocket engines as before and don't build, test and debug larger ...


2

There is a serious advantage to being able to make complex decisions, perhaps even moral decisions, on board the spacecraft without any lag due to the speed of light. For the sake of argument, imagine a robotic emissary encounters life on the nearby Jovian moon Europa, which immediately offers some kind of complex moral test to determine whether they will ...


2

A footnote on page 82 of Pellegrino and Stoff's Chariots for Apollo reads "Lynn Radcliffe explains: The Teflon seals and other materials in the [lunar-module ascent] engine were good for only forty days after exposure to live propellants, so if you test-fired it or let live propellants get anywhere near the seals, you had to do you mission with forty ...


2

Have a look at Sutton (7th edition online here) Chapter 3.4 The converging nozzle section between the chamber and the nozzle throat has never been critical in achieving high performance. The subsonic flow in this section can easily be turned at very low pressure drop and any radius, cone angle, wall contour curve, or nozzle inlet shape is satisfactory.


2

Model rockets are often not very smooth. The skin friction term comes from the laminar portion of the Cf vs Re No. curve. It is highly unlikely that model rockets have much laminar flow. Fins may not have rounded leading edges or sharp trailing edges. Surface finishes may be very rough, depending upon how much time (and skill) the rocketeer put into the ...


1

Apart from everything else that's been mentioned: many times, one of the questions that the mission is trying to answer is "how well can humans do X in space" for some value of X. It should be reasonably obvious that you need some humans in space in order to answer such questions. NASA's website currently lists some 249 such experiments (plus 40 &...


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