75

Are there any satellites in geosynchronous but not geostationary orbits? Yep, lots! Apparently there are various advantages to being synchronous even when oscillating wildly in position above/below the Earth's equator (up to +/- 60 degrees!) After seeing the figures below in A New Look at the GEO and Near-GEO Regimes: Operations, Disposals,and Debris (...


41

Yes, I've done it myself in my backyard in suburban Houston. During a spacewalk in ISS increment 50, an MMOD shield intended for the axial port of Node 3 was lost. It's visible in this video floating below station. It ended up reentering about six months later. A few weeks after it had been lost, I noticed that it would be visible from my house, with a ...


41

Could you fit all six into a FH fairing? If not, would a slightly larger one be enough? I can't find dimensions for GPS III sats, but this Lockheed Martin image shows how much of a Delta Medium 4-meter fairing is taken up by a single one: Looking at the dimensions of the fairing in the Payload Guide, I think the satellite is about 5m long by 2.5m wide. ...


36

If the satellite is close to the Earth, a last bit of fuel is used to de-orbit it so that it burns up. If it is farther out, it is moved to a retirement orbit out beyond the used orbits. The last thing done after moving it to the retirement orbit is to permanently disable the communication system so that it doesn't randomly transmit stuff and put noise on ...


29

Note: This answer is based on a source from 2001. It provides a lot of background as a historical overview, but it does not take into account recent changes in the program. Please review the end of Organic Marble's answer for a fuller perspective. Initially, it began as a temporary program. In the late 1950s, the US military needed accurate and timely ...


28

The only satellite I know of that was shaped to have low drag was GOCE, which orbited at 250 km. Since it was vital to ensure that the measurements taken are of true gravity and not influenced by any movement of the satellite, this unique five-metre long arrow-shaped satellite had none of the moving parts often seen in other spacecraft. The satellite, ...


21

A satellite that is retired ordinarily and not expected to reenter will be passivated. The aim here is to minimize the amount of energy stored in the spacecraft, ideally it will be a dead rock floating in space, far from anything it could interfere with. This includes deactivating the comms to stop interference as zeta mentions, but also emptying the tanks ...


20

Solar panel technology seems to have caught up with power requirements on the satellite. Since price of components is really no object when building a system like this, super expensive panels with efficiency ratings of up to 40% can be used. The trick to engineering something properly is using just the right amount of materials, as the old maxim goes "Any ...


18

The specific needs of the military may not be served by civilian weather satellites. Specifically, the DMSP started as a classified program that supported the Corona spy satellite program. Its purpose was to predict cloud cover over foreign countries so that the expendable film in the Corona satellites would not be used up taking pictures of the tops of ...


17

Lagrange points as I understand it are points in space between 2 objects where the gravitational pull between them is effectively equal. A quick check of Wikipedia's Lagrangian point or any article will show that only one of the five Lagrange points are "between (the) two objects". The pulls are not equal, they balance in such a way as to allow for an orbit ...


14

Could a slower or smaller rocket take advantage of lift if all the stages had wings? Wings on the first stage can be useful; the Pegasus air-launched rocket has wings on its first stage that provide some lift. In most cases wings aren't worth using on orbital launchers; they add drag and weight that usually isn't compensated for by lift. Wings on upper ...


13

Defining "retrieval" as "returning a commercial satellite to earth" then as of this moment there is no known capability to do that. (Ground-ruling out capsules like Dragon that return themselves with internal cargo). As you mention Shuttle was designed for that but it was decades since it performed that function. One could speculate about the X-37 and ...


12

This largely depends on purpose/application, but if you want it just to "be in orbit" then the answer is "not very precise at all.". Or quantifying better, the periapsis speed must be between the speed of circular orbit and escape speed which is $\sqrt{2}$ of that - so about 40% of "slop". Of course satellites aren't of much use if you can't communicate ...


10

The degree of orbital shadowing experienced by an orbiting object with small orbital altitude is determined by its beta angle (normally used in reference to LEO objects but the concept applies to lunar orbiters as well). The angle is taken between the satellite's orbital plane and the vector to the Sun. Depending on the value of the beta angle, a satellite ...


10

Basically they are not quite in the same plane. As a satellite raises or lowers, not only does it change the relative position within an orbital plane, it also will slowly shift the longitude of the ascending node with respect to the other satellites, called the "Nodal Precession". In fact, this happens every day. There is a lot in this, but the bottom line ...


9

The disk is in no sense in orbit if it stays above a fixed location on Earth at such a low altitude. Basically the thrust would need to do all the work to hold it up against Earth's gravity. So such a disk has an area of $5000^2\pi\ \mathrm{m^2}$ and so a mass of $2.5\pi\times 10^8\ \mathrm{kg}$ with your estimate for the area density of the disk. It would ...


8

Though it seems noöne has spun an entire rocket stage to slow it, something similar has been tried. The long-defunct Rotary Rocket company was developing the Roton™ reüsable single-stage-to-orbit launcher that would use helicopter-like blades to slow and land. A bit more info on it can be found on Wikipedia. Alan Radecki via Wikimedia Commons, GFDL / CC ...


7

You are correct in your understanding, Once it reaches the vicinity of the South Pole, specifically the most southern point in its orbit it will start going north. The reason they said north to south is to differentiate it from the orbits going west to east (which by the way stay west to east). This is also very neatly demonstrated by the satellite's ...


7

There are actually quite a few methods satellites use to avoid collisions. Under international space law (outer space treaty) no one and no country "owns" an orbit which mean technically it is a free for all. However, any organization with a satellite is generally pretty committed to not having it get hit, so conventions are followed. First tracking, the ...


7

When calculating the future orbit of an artificial (Earth) satellite, is the moon's gravity significant or insignificant? It's a great question! Of course everyone's definition of "significant" will be different. Gravity is a long range force, it never goes to zero, and decreases only as $1/r^2$. Nothing blocks it either, so basically everything pulls on ...


7

There is no circular orbit that has a share of 50:50 between night and day. The possible times are a bit less than 50% to 0% night or, respectively, a bit more than 50% day to 100% day. The two extreme cases are: an orbit that is aligned with the terminator (the border between night and day on the surface) is in perpetual daylight. an orbit that passes ...


6

Vertically launched rockets need thrust (force in the direction of motion), not lift (force perpendicular to it). Wings can only provide lift and drag (force against the direction of motion), and a vertically launched rocket needs neither of those things. What an orbital rocket does need is speed so the less drag the better.


6

Clarke proposed geostationary communications satellites in a letter to Wireless World magazine in early 1945. Later in the same year he expanded on this idea in two more papers, one of which was published as Extra-Terrestrial Relays in Wireless World in late '45. The article mentions the orbital altitude needed for a 24-hour orbital period (42000 km ...


6

The only stable points that orbit at the same speed as Earth are the L4 and L5 points, as you mention, but there are some unstable ones as well. See this pic from NASA: L4 and L5 remain ahead of and behind the Earth, whereas L1, L2 and L3 are inherently unstable. From your question, I'd suggest L4 and L5 would be best suited, unless you really need ...


6

The temperature of space near earth is about as 10 degrees Celsius, but much cooler in interstellar space. It depends. A better value is 5.2 degrees Celsius, and that assumes a macroscopic perfect blackbody that rotates rather quickly. The temperature of a sub-microscopic object in near Earth space would more likely be in the tens of thousands of degrees. ...


6

Yes The orbit you are talking about is one of the Lagrangian Points, the L2 point to be more precise. As a matter of fact, a few satellites are there - and, most relevant to this question, the James Webb Telescope will be placed there. Note that the L2 point is a point of gravitational equilibrium, but isn't actually a stable point. That means that ...


6

You are describing the Local Vertical Local Horizontal (LVLH) frame of reference. It is used to describe the orientation of the spacecraft in relation to the Earth's surface. For example, if you wished to point an instrument at the point on the Earth directly below the spacecraft, the craft would fly in a constant LVLH attitude. But its inertial attitude ...


5

I got curious and read this, it makes plenty of sense to me. http://www.jamesoberg.com/sts88_and-black-knight.pdf The suggestion is that many of the photos are really of a bit of space debris from STS-88. The author explains that the hype is just that, hype. The intense passion to want to believe so badly that this is something alien, clouds any type of ...


5

Assuming the goal is the Earth orbit (the outcome could be different for Mars), the kinetic energy in a low orbit is about 30 MJ/kg. There is little use to lift a rocket to the, say, 20 km level using air-breathing engines and wings in order to supply 0.2 MJ/kg of potential energy before starting the rocket motors. Also the initial kinetic energy (e.g. 1 % ...


5

The rocket passes through the dense layers of the atmosphere in the first tens of seconds after launch. Further, these wings are ineffective. Baikal (on render) is a reusable rocket plane. Most of the time being in dense layers of the atmosphere.


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