# Tag Info

38

Primarily, locations of spaceports would change. California, not Florida would host the NASA's main launch site. Russia would be in slightly better position, able to send rockets over the Black Sea, nicer inclinations than currently available from Baikonur - although Vostochny wouldn't happen or would be closer to Chita. ESA could forget about French Guiana, ...

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 ...

29

So let's break down the answer into bite sized chunks... How do you transfer a spacecraft from one solar system body to another? There are two main things you need to do. Set up an orbit that intercepts the orbit of your target planet/moon. Time it so that your spacecraft intercepts the target orbit at the same time as the planet/moon you're trying to ...

27

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 ...

23

The thing your're missing is that the Hohmann Transfer orbit takes time, and both Mars and Earth are moving around the sun. For the Hohmann Transfer orbit to work, the position of Mars at arrival has to be opposite the point of of Earth at Departure. The following image depicts Earth's and Mars' orbit as circular, rather than elliptical to simplify ...

23

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

Does pork-chop plots exist for Earth-Moon System? No, because the concept doesn't make much sense. The Earth-Mars configuration and Mars' eccentricity makes the cost to send a vehicle from Earth to Mars vary by a huge amount. Pork chop plots are a useful way to visualize these huge variations. The cost of sending a vehicle to the Moon on the other hand ...

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

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 ...

9

Yes, according to Mike Collins (but from lunar orbit, not on the surface). The earth as seen from this distance - nearly a quarter of a million miles - is an unforgettable sight. To begin with, it looks tiny, the size of your thumbnail held at arm's length. It is mostly ocean and clouds, the blue and white dominating the brownish-green of ...

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 ...

5

As far as I know, only NASA (since you asked for the agency) through its High Definition Earth Viewing (HDEV) Experiment gives the live coverage of the Earth from the ISS. It might not be up for all the time and they sometimes switch to previously recorded videos in case of technical problems but this is only source I know available in the public domain. ...

5

I don't know if any Apollo astronaut talked about it, but in the famous "Earthrise" photo taken from lunar orbit on Apollo 8, landmass (the west coast of Africa, I believe, at the lower edge of the sunlit portion of Earth) is distinguishable from the oceans:

4

I agree with Ingolifs' answer; you can create a porkchop plot for a transfer between any two orbits. For an Earth-Moon porkchop you could pick either a point on the Earth's surface or a particular low Earth orbit as your start. For example, here's a porkchop plot showing the delta-v required for transfer from Apollo 13's initial Earth orbit to the Moon (...

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 ...

4

Deep space missions would not change much. The spacecraft needs energy to climb out of the gravity well. It starts with kinetic energy (speed) but as it climbs higher it's exchanged for potential energy (height). The higher the orbit, the slower is motion of spacecraft relatively to the Earth. A LEO orbit needs about 7.9 km/s but at a GEO orbit satellite is ...

3

Much of engineering is about compromises. One can find an ideal solution, like a Hohmann transfer orbit. Yes, that is the most fuel efficient way to get from earth orbit to Mars orbit. It is like the top of a rounded mountain. That is the peak, but there is a lot of ground near the peak that is almost as high. Maybe you are willing to give up a bit of ...

3

Does J22 represent the rest of Earth's quadrupole moment? With a more usual notation ldegree, morder, there are the zonal l2m0, tesseral l2m1 and sectoral l2m2 spherical harmonics, but you probably already know. What does J22 look like? What is its shape and symmetry? Here's what I get for l2m2: For comparison, here's what I get for your "acceleration ...

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 ...

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 ...

2

The moon has about 7 x 10^22 kg of mass. The earth has about 6 x 10^24 kg of mass. So the Earth masses about 10^2 (aka 100) times more than the moon. To stay in orbit around the Earth, you've got to go faster than about 7800 meters per second sideways. To stay in orbit around the moon, you've got to go faster than about 1650 meters per second sideways. So ...

2

Wikipedia actually goes into some detail regarding the components of Earth's gravitational force field. In the Wikipedia reference we do not have $J_{m,n}$ for $m>n>0$. Rather this term is broken up into a cosine component $C_n^m$ and a sine component $S_n^m$. This table gives results from one on a series of models called the JGM models, developed by ...

2

PIA10244: Earth and Moon as Seen from Mars article you link to links to the JPL image catalog page PIA10244: Earth and Moon as Seen from Mars which says: The High Resolution Imaging Science Experiment (HiRISE) camera would make a great backyard telescope for viewing Mars, and we can also use it at Mars to view other planets. This is an image of Earth and ...

2

There is a nice Wikipedia image of Earth (ø = 12,756 km) and Moon (ø = 3,476 km) at the same scale. When you look up to the full Moon at night with a clear sky you are able to see many details. The astronauts looked up to the much bigger Earth at the same distance. So they were able to see much more details of Earth than we see of the Moon. The famous ...

2

Quite possibly Upon learning that Mars did have surface water at some point, you have updated your question to ask if Mars would be a good approximation for Earth if Earth had little to no water, or if the water had been missing for a period of time. Conversely, try looking at areas of the Earth that have had little to no water, or where the water has been ...

1

To answer your question it is neccessary to compare the escape velocities of the Moon and the Earth. The escape velocity does not depend on the mass $M$ of the celestial body alone, it also depend on its radius $r$. $v_2 = \sqrt{\frac{2GM}{r}}$ $G$ is the gravitational constant. The escape velocity $v_2$ is 11.2 km/s for the Earth and only 2.3 km/s ...

1

Stellarium is a general planetarium program which is available for Linux, MacOS X and Windows and is pretty easy to use. Moving the mouse to the left side of the screen pops out options to change the date/time and to search for an object. I set the time to 2106-10-16 and searched for 'Mars' and got the following screenshot: Included in the admittedly large ...

1

Spacecraft launches are not AFAIK the main reason for changes in Earth's angular rate and angular momentum. Regarding the angular velocity, you can check DUT1, which is defined by Wikipedia as follows: The time correction DUT1 (sometimes also written DUT) is the difference in seconds between Universal Time (UT1), which is defined by Earth's rotation, and ...

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