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209 votes
6 answers
22k views

Can I borrow a lunar rover?

According to Wikipedia there are 3 LRVs sitting on the moon, in very well defined locations. Would China, or whomever gets to the moon with a person next, be able to get in and drive around in an LRV ...
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164 votes
2 answers
262k views

What computer and software is used by the Falcon 9?

I don't know if this would be public, but what CPU / Microcontrollers are used and what software do they run on the Falcon 9? Do they use an OS or is it just bare metal programming? I found some ...
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  • 5,133
161 votes
3 answers
24k views

How did the Apollo computers evaluate transcendental functions like sine, arctangent, log?

Navigation with a sextant or maneuvers using gimbal angles might be two examples of cases where an Apollo computer might need to do trigonometry. Trigonometric functions like sine, arctangent, etc. ...
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  • 148k
146 votes
12 answers
177k views

Couldn't I escape Earth's gravity traveling only 1 mph (0.45 m/s)?

It is said that in order for an object or a projectile to leave Earth's gravitational pull, it must reach Earth's escape velocity, meaning reach a speed of 7 miles per second (~11 km per second). Well,...
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  • 1,775
143 votes
5 answers
40k views

Nudism in space: Why wear clothes anyway?

Currently, doing laundry in microgravity is an unsolved engineering problem. The result is that clean clothes on the International Space Station have become a consumable resource. Clean clothes get ...
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  • 9,196
126 votes
4 answers
33k views

Do the planets really orbit the Sun?

We often say that the planets orbit the Sun, which is usually a reasonable approximation. But in reality both Sun and the planets orbit the center-of-mass/center-of-gravity of the whole solar system, ...
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  • 1,757
121 votes
1 answer
8k views

How many extraterrestrial bodies have hosted a "lander" which returned images?

For the purposes of this question, we will consider a "lander" any probe which was sent to the surface of an extraterrestrial body or entered the atmosphere to a point which exceeds an air pressure of ...
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  • 23.6k
114 votes
6 answers
25k views

What makes Ada the language of choice for the ISS's safety-critical systems?

We have it on good authority that Ada is widely used for "safety critical software" on at least the US side of the International Space Station. Of all the possible languages to choose from, what are ...
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  • 148k
114 votes
4 answers
19k views

What is the purpose of having a countdown during a rocket launch?

Every rocket launch has a countdown. But what purpose does it serve?
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  • 18k
113 votes
13 answers
60k views

What are the choices today for orbital mechanics simulation software?

I used to be familiar with the various choices out there for orbital mechanics simulation software. Alas, those days are gone. What are the choices today, preferably sorted by platform? This ...
111 votes
8 answers
28k views

If the astronauts on Apollo 11 had landed safely on the moon but could not take off, would there have been a rescue mission?

Say they landed on the moon but discovered the ship was damaged during the landing and they could not launch again. What would have been the plan? Would another crew have been sent to rescue them? ...
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  • 1,249
104 votes
3 answers
100k views

How did NASA achieve their live TV broadcast in 1969?

In 1969, NASA not only went to the moon, but broadcast the whole thing live on TV. How did they achieve the TV broadcast? What technology did they need to use to send a video and audio signal from ...
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  • 1,035
102 votes
3 answers
26k views

Is this "Attach Orbiter Here / Note: Black Side Down" sign on the Shuttle Carrier Aircraft real?

I found this image online, but is it a real message?
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  • 2,416
97 votes
1 answer
18k views

Who was the first human to sleep - perchance to dream - on the Moon?

Incidentally I don't mean "on the lunar surface, asleep laying on the surface of the moon" :) So (A) who (if anyone) was the first human to actually be asleep (that is to say, presumably inside the ...
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  • 1,604
95 votes
3 answers
137k views

What happens to the Falcon 9 second stage after payload separation?

In a Falcon 9 launch, the second stage looks like it achieves orbit along with the payload. But is that impression accurate? Does SpaceX need to do anything to deorbit the stage? I can see a few ...
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  • 122k
91 votes
4 answers
16k views

How did Apollo 16 capture this full photograph of the Moon's far side?

Apollo 16 famously photographed the far side of the Moon, as seen below. This seems odd to me. Apollo 16 orbited the Moon at an orbit of only 100 km. It seems too close to get this kind of a ...
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  • 119k
89 votes
4 answers
23k views

Why destroy Juno at the end of the mission?

As follows from the mission timeline: Launch - August 5, 2011 Deep Space Maneuvers - August/September 2012 Earth flyby gravity assist - October 2013 Jupiter arrival - July 2016 Spacecraft will orbit ...
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89 votes
6 answers
16k views

How much bigger could Earth be, before rockets wouldn't work?

hint: Apparently the Tsiolkovsky rocket equation does not actually say that you can launch a conventional rocket into orbit around an arbitrarily large and massive body. I'm looking for a number ...
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  • 148k
86 votes
3 answers
22k views

Could an Apollo astronaut stand up if they fell on the moon?

I was watching old Apollo footage and noted how astronauts on the moon had a very particular gait most likely due to the poor flexibility of the EVA suits, low gravity, and need for safety. I was ...
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  • 1,133
85 votes
8 answers
15k views

Why do most space probes survive for far longer than they were designed for?

Looking back to Opportunity (Rest In Peace, little friend), it was apparently designed to operate for 90 days but it ended up going for 16 years which is approximately 64 times longer than the ...
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  • 813
84 votes
7 answers
22k views

What can the KSP game actually teach about spaceflight and orbital mechanics, and what are its limitations?

I have seen at least several different users mention that they've found Kerbal Space Program helpful to understand issues of spaceflight and orbital mechanics. According to Wikipedia: While the game ...
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  • 148k
81 votes
5 answers
12k views

Could "peak Apollo levels" of support have gotten NASA astronauts to Mars in the 1980's?

In an "alternate universe" where NASA continued to receive a mandate, funding and public support at say peak Apollo levels, could another ten or twenty years have gotten boots on Mars, with astronauts ...
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  • 148k
78 votes
4 answers
12k views

How do astronauts on EVA deal with nose itching?

It must be absolutely torturous if your nose starts itching and you can't scratch it for several hours, when you're on EVA. How do astronauts deal with it? Are they undergoing a special training, or ...
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  • 52.7k
76 votes
6 answers
26k views

Is the SpaceX Falcon Heavy payload (a Tesla car) space junk?

Yesterday SpaceX succeeded in the first Falcon Heavy launch, but the payload, a Tesla car has no real useful purpose (except for company prestige). Thus, can it be considered as space junk ? How long ...
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  • 899
76 votes
3 answers
51k views

Was the NOAA-N Prime satellite really dropped on the floor?

Recently, Donald.McLean posted this image in The Pod Bay, the site chat room: It's a rather disturbing image once you think about it for more than about half a second. Did it really happen? What ...
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  • 17.8k
75 votes
9 answers
26k views

A starship is traveling at 0.9c and collides with a small rock. Will it leave a clean hole through, or will more happen?

Say there is a football sized rock in the path of the ship. Will it create a football sized hole through the ship in the blink of an eye, or will more happen? The ship would be filled with metal, ...
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75 votes
3 answers
44k views

What will be the effect if we stand on Jupiter?

As we all know Jupiter is a gaseous gas giant and it has a large mass, almost twice the sum of all other planets in the Solar system. So, if it happens that we go to Jupiter, and, as we know it does ...
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74 votes
5 answers
12k views

Difference between BlueOrigin and SpaceX rocket landings?

So, SpaceX has finally landed their booster back to the land. BlueOrigin has achieved the same thing in a recent past, but I have read so many people commenting and criticizing the comparison of ...
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74 votes
1 answer
17k views

Why did some Apollo missions carry a grenade launcher?

According to ALSEP Flight System Familiarization Manual, p. 2-166, some Apollo missions carried a grenade launcher and 4 grenades. What were these used for?
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  • 46.6k
73 votes
7 answers
16k views

Why is the American space program launch site based in Florida and not Texas?

In other words, why didn't NASA make their main space launch area in Texas? It has a point below the 30th parallel, which means that it is close enough to the equator. Why did NASA pick Florida?
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  • 1,685
73 votes
5 answers
19k views

Why is it easier to escape the solar system than get to Mercury or the Sun?

It has been mentioned several times on this site that it is "easier" (less delta-v, and hence less fuel) to reach the escape velocity of the solar system, than to reach the planet Mercury or ...
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  • 46.6k
72 votes
10 answers
54k views

Why is SpaceX considering Methane as fuel for their next engine, the Raptor?

Currently, SpaceX has developed the Merlin 1 family (1B (Falcon 1), 1C (Falcon 9 v1.0), 1D (Falcon 9 v1.1/F9-R/Falcon Heavy), vacuum versions and sealevel versions) which are LOX/RP1 based. (75-...
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  • 76.7k
72 votes
2 answers
70k views

When will New Horizons overtake Voyager 1 in distance from the Sun?

Basically, what the title asks. To my understanding, New Horizons is currently the fastest spacecraft that's moving away from the Sun, with arguably only Helios-A and Helios-B possibly faster still, ...
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  • 75.6k
71 votes
9 answers
15k views

Which country borders are visible from space?

You can see the borders of North Korea with China and South Korea at night from the ISS since unlike their neighbours, they have almost no light. That got me thinking, which other country borders (of ...
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  • 12.4k
71 votes
5 answers
19k views

Why do SpaceX Starships look so "homemade"?

Maybe this is not possible to answer, but I was hoping there was some reliable information available on this. It seems to me that the SpaceX Starship rockets have sort of a homemade quality to them, ...
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71 votes
6 answers
33k views

Why does the ISS have to be destroyed?

ISS might be destroyed soon, de-orbiting for a controlled reentry into the Pacific Ocean. Why isn't simply pushed away from Earth to an outer stable orbit (not sure if it's possible) or even into an ...
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71 votes
2 answers
7k views

Can a human land on Deimos using pressurized deodorant cans?

Can an astronaut use deodorant sprays which contain pressurized butane as cold gas thrusters to land on Deimos from Deimos' orbit? If yes, how many cans would be required to get 5 m/s of delta-v for a ...
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  • 2,348
69 votes
4 answers
24k views

Could we breathe an atmosphere that is not nitrogen based?

As I understand it, the important part of Earth's atmosphere that we breathe is the oxygen. However, Earth's air is only about 21% oxygen with the rest made up of about 78% nitrogen and 1% other gases,...
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  • 791
69 votes
4 answers
10k views

Why did it take so long to notice that the ozone layer had holes in it? Which satellite provided the data?

Wikipedia says: The discovery of the annual depletion of ozone above the Antarctic was first announced by Joe Farman, Brian Gardiner and Jonathan Shanklin, in a paper which appeared in Nature on May ...
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  • 148k
69 votes
3 answers
13k views

Did Feynman cite a fallacy about only circles having the same width in all directions as a reason for the Challenger disaster?

In a Math Overflow post about mathematical fallacies it was stated that: Richard Feynman regarded the mistake that a "circle is the only figure which has the same width in all directions" as one ...
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  • 1,101
69 votes
1 answer
8k views

Why did the Apollo 13 crew extend the LM landing gear?

From the Apollo 13 radio transcript, as they're going through the Lunar Module activation checklist: 060:58:58 Lousma: Okay. The only item on page 10 is to deploy the landing gear. 060:59:06 ...
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  • 11.6k
68 votes
1 answer
4k views

How far could we send someone before they get a lethal dose of radiation?

Given current technology, how far could we send someone before they get a lethal dose of hard radiation? What if they don't need to make a return trip? I know that last I had heard, Mars was too far ...
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  • 787
67 votes
17 answers
21k views

Why is using a space elevator cheaper than rocket power?

Why is rocket power so much less efficient? In both cases you want to lift a given weight a certain height. What does climbing a tether give you that you don't have when using rockets? Wouldn't a ...
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66 votes
8 answers
39k views

Why would SpaceX not use parachutes for the final descent of the first stage?

According to what I've read, SpaceX tried to use parachutes to recover the first stage of the Falcon 9, but it did not survive reentry. Now they plan to use 2 separate rocket burns to land: Reentry ...
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  • 5,133
66 votes
6 answers
26k views

Can I drive Elon Musk's Tesla after it's been in space for 100 Years?

We know that the the payload of the maiden Falcon Heavy flight will be... Elon Musks's Tesla Which will be placed in "Mars Orbit" Assuming it is serviced and road ready when launched with the keys in ...
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66 votes
2 answers
8k views

What was Apollo 13's "Little Jolt" after MECO?

Disclaimer: This is a question about the 1995 film Apollo 13; I know Hollywood should always be taken with a moon-sized grain of salt, so the question should read as both "Is this true" and "What was ...
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66 votes
1 answer
12k views

Why do astronauts wear heels?

I was reading another question on the site when I noticed the EVA suit sports heels. Why do they put heels on space suits? (cropped detailed view)
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  • 737
65 votes
4 answers
15k views

Why do ISS crew members often cross their arms?

I am watching live stream from ISS to follow the return of two ISS crew members, Thomas Pesquet and Oleg Novitskiy. At several moments, they crossed their arms in a not really natural way: Why do ...
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  • 2,010
65 votes
3 answers
9k views

Is there no physical security in space, other than being in space?

I saw Gravity the other day and while visually and emotionally compelling, and besides the liberties taken with orbits, something else struck me as unrealistic, but I'm not sure if it is or isn't:...
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  • 2,767
64 votes
4 answers
15k views

How did people know how to build the first space ship?

How did the early designers of spacecrafts have any idea what space was actually like? How was a vessel ever constructed that actually flew through Earth's atmosphere without burning up, and then ...
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