Hot answers tagged

72

In your simulation, the camera (or the viewers perspective) is stationary in what seems like in an altitude of a geostationary orbit. However the ISS is not stationary, it is travelling 7.6 km/s. It completes one orbit in 92 minutes. The ISS orbiting is giving the illusion that the Earth is spinning that fast. Note: The Earth does still spin while the ISS ...


37

You're right: this has issues. You can insert a station into a circular orbit halfway between Earth and Mars, but because this has an orbital period also in between those of Earth and Mars, your station won't be in a usable position most of the time. So you'd have to fill the orbit with several station to always have one reasonably close. The fuel is also ...


33

It isn't the actual level of charge (potential) that causes electric shock. but being connected to two things (like your iron and the ground) that are at different levels. Hence why birds can sit on a 750kV overhead line and not fry. The earth wire in a domestic system exists to keep all exposed metal at the same potential. Grounding everything to the frame ...


26

Initial and Bonus Answer: With a volume of 609.31 M^3 and an empty mass of 15,500kg (13,500 kg empty weight plus 2,000kg for the attached Instrument Unit), J002E3 is Apollo 12's S-IVB stage (designated S-IVB-507). It was intended to be placed in a heliocentric orbit following Apollo 12's TLI Burn. Due to insufficient propellant, however, it ended up ...


22

As others have noted, the ISS orbits the earth extraordinarily quickly, and that explains the discrepancy. However, there may still be a small error in your simulation. Whether or not there is an error depends on where you intend the "camera" to be. My suspicion is that your simulation was created as follows: Make a sphere at the origin, inclined 23 ...


22

I would say it's probably Envisat. It is definitely the heaviest although i'm not sure if it is also the largest piece volumetrically. We had a full scale 'mock up' at our faculty and I can confirm that it is absolutely massive! They have been thinking about ways to deorbit it for quite a while now since a collision involving this large of a satellite could ...


20

"Earth" doesn't work the way you might think. In any case, on a vehicle of almost any kind, "earth" is replaced by "metal chassis". Your question is based on a very common misconception: that electricity wants to return to earth. Actually, electricity wants to return to source. For instance, electrons at a battery's negative terminal want to return to ...


13

Answer for Bonus question Not entirely sure if indeed the biggest (in heliocentric orbit), but bigger than roadster for sure: S-IVB, the third stage of Saturn V rocket that was used for Apollo lunar missions (height 17.81m, diameter 6.6m) https://en.wikipedia.org/wiki/S-IVB There are few of them in heliocentric orbit. https://en.wikipedia.org/wiki/...


13

The ISS takes approximately 90 minutes to circle the Earth. This presumably results in the higher apparent speed of rotation.


13

It's hard to guess what is in the mind of another contributor, but... Using a cycler model could involve a network of space ports, and the cycler would take the role of a "midway" space station (it taking care for the cargo for the portion of the journey between Earth and Mars) In Earth orbit, there would be a staging post or spaceport. Launch vehicles ...


11

There is a nice image of Earth (ø = 12,756 km) and Moon (ø = 3,476 km) at the same scale. It is a matter of size and distance. The Apollo Lunar Module shown in the first image of the question is very close to the Moon, some hundred kilometers only but very far away from Earth, about 360,000 km. But the distance of the camera to the Moon is much bigger in ...


10

Supplemental answer, so I can post a picture: Here's a picture of the Moon and Earth taken by the lunar orbiting Chinese satellite Longjiang-2. Note the similarity of the size of the Earth to the Apollo picture. The Chinese satellite is farther from the moon than the Apollo modules were when the picture in the question was taken. Noticed it here: Was this ...


8

The answer is given in the thread linked in @KaushikGhose's comment: The space station solar arrays operate at 160 VDC. When the arrays are producing power, the station structure will also tend to float to a voltage close to the array voltage. Under these conditions, the space station could be subjected to problems like arcing from its ...


8

Hydrogen and Helium, mainly, at rates of 3000g and 50g per second, respectively. The process is called "Jeans Escape", and is due to the atoms being light enough to gain a significant velocity from radiation. The effect is really small - 3Kg of Hydrogen and 50g of Helium per second is tiny compared to the mass of the atmosphere. Also notice how big a ...


7

Fuel and time probably give different answers and it also depends on whether you want proved current hardware, engineering studies or wild speculation. Let's maybe consider some options: Chemical rockets a small rocket with a large fuel tank, using a high $I_{sp}$ fuel mix such as liquid hydrogen and liquid oxygen is an option. Freed of the need for enough ...


7

Yes, but no. Angular momentum is conserved, and since we launch rockets roughly tangentially from Earth's edge there will be a counter-spin imparted. While an occasional rocket is launched "backwards" (retrograde, The strange orbit of Ofeq 11 - how does it (actually) do this?) most go roughly prograde while some go polar. I don't yet have my license to ...


6

Exactly at the center-of-mass of the Earth there is no net gravitational force. Gravity comes from mass, and all the mass of the Earth is evenly distributed around the center-of-mass (by definition), so all the forces cancel out. As you get deeper and deeper, the net gravitational force falls -- linearly if density is constant. In practice, of course, you ...


5

In this answer, I'm going to assume the tunnel is a perfect vacuum and there's no intense heat or pressure. This is a thought experiment. If you and John fall at the same time, you guys will meet approximately 20 minutes after you jump into the tunnel. Depending on how wide the tunnel is, you guys will most likely collide at a velocity of around 11 km/s. ...


5

can we hang a really large wire from space to earth? That depends how large that wire is. If it's 500 km long, then no. Gravity will make that wire come down. However, if the wire is long enough to reach an altitude of about 35,000 km, then the wire can be stable through tension as the centrifugal force of the Earth spinning is strong enough for the wire to ...


5

Yes it's possible, and known ... at Pluto. What are officially called the (four known) smaller moons of Pluto are actually orbiting the center of mass formed by Pluto and its large moon Charon, which is outside both Pluto and Charon. Wikipedia includes an animation of all the known moons orbiting Pluto. The small moons are all much farther away from the ...


4

This is an interesting question! tl;dr: I don't know about artificially maintained orbits, but for uncontrolled orbits Earth's strong oblateness and the Moon's gravitational perturbations will not allow for an orbit parallel to the ecliptic to remain that way. Near GEO: We're looking for an Earth orbit with an inclination of 23 degrees, and a ascending ...


4

Besides the role of any past photosynthetic life on Mars (see MSalters's answer), excess free oxygen could also have appeared through inorganic processes. Such processes may have been promoted by solar radiation bombarding the atmosphere and surface, releasing oxygen atoms. This is a common theme in what follows. Space.com gives several possible ...


4

Is a midspace space station between Earth and Mars practical? Here's a naive view: The problems with notions like a "halfway" station is that the locus of points halfway between Earth and Mars is probably a thick disk with an radius about equal to the average of the average of Earths and Mars orbital radius. Mars also has the second most eccentric orbit of ...


3

Pretty sure that it is the "Inory Eye" camera as mentioned in the Planetary Society piece: However, the Longjiang-2 transceiver also carried an onboard student-developed camera, dubbed the Inory Eye (a note on the name here) and controlled by a tiny circuit board, which has returned a string amazing images of the Earth and Moon, as well as the lunar ...


3

That is how it is commonly used. If you were in a parking orbit around Mars, it is imaginable that the burn that brought you on the transfer back to earth wold be called a TEI. The TEI from Apollo is also a deceleration wrt. to Earth, just like a TEI from Mars would be a deceleration wrt. the Sun. In 2004, from outside the Earth-Moon system, the Stardust ...


3

Solid angle $\Omega = 2\pi(1-\cos \theta)$ $\theta = APO $ $(OA)^2 + (AP)^2 = (OP)^2$ OA = r - radius of earth and OP = r + h (height of satellite) $r^2 +(AP)^2 = (r+h)^2$ $AP = \sqrt{2rh + h^2}$ $\cos \theta = AP / OP =\frac{ \sqrt{2rh + h^2}}{r + h}$ $\Omega = 2\pi \left( 1-\frac{ \sqrt{2rh + h^2}}{r + h} \right)$ For r= 6378 km and h = 400 km ...


2

According to @RobJeffries' answer: Even in favourable conditions, the optical depth of the Martian atmosphere is usally somewhere between 0.5 and 1 per airmass. (Petrova et al. 2012; Lemmon et al. 2014) and is nearly wavelength independent. This corresponds to a reduction in flux to between 37% and 60% of its value above the atmosphere. This compares to a ...


2

First of all, the distances in the solar system are absolutely tiny compared to the distances between stars. To the casual observer, the celestial sphere (by which I mean everything in the sky except for the Sun and planets) will look absolutely identical to how it does on earth, or pluto for that matter. From a specific arbitrary point on mars, the sky ...


2

Plenty of probes have taken photos of earth from deep space since Voyager. The one from Saturn's orbit (Cassini Spacecraft) and the one taken by the Juno probe shortly after launch stand out as quite similar to the original pale blue dot pictures. This one (also from Cassini) is visually quite stunning: http://www.planetary.org/multimedia/space-images/...


2

They were only in orbit for a few years each in the 1960s, and thus fail the "currently" test, but the Echo1 and Echo2 satellites deserve some mention. https://en.wikipedia.org/wiki/Project_Echo Basically aluminized Mylar balloons, Echo1 had a volume of $14,800 \text{ m}^3$, while Echo2 topped out at $36,000 \text{ m}^3$ Echo2 was actually test-inflated ...


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