Tag Info

41

More or less. While the ISS is below the satellites use for TV transmissions, it is passing by so fast that the coverage will be highly intermittent, meaning that you would be able to watch a channel for only a couple of minutes, have black outs over the oceans, and repeat. Other notable differences would be: Normal satellites receiver are "fixed": The ...

34

What would you notice first? Satellite navigation: immediately (depending on how often you use satnav) TV: immediately (depending on how often you use TV). Even if you don't use satellite TV yourself, your TV provider may receive some of its channels via satellite within a day or so: weather forecasts no longer include satellite imagery, and accuracy goes ...

25

You can't replace the Internet like that since Internet is also a collection of protocols for routing and addressing, and transmitting users' data. You can try swapping fiber optic links for LEO sat comm ones, but throughput will invariably suffer and connection will be less reliable. Satellites' transponders are the bottleneck - instead of an hierarchy of ...

25

Nodal precession doesn't matter for a plane of satellites like this, they will rotate around in unison, so the coverage will remain the same. Okay, so why the unusual dual inclination constellation? The inclination of a satellite band tends to let you know what latitude it will work best at. A 0 degree satellite works best at the equator, a 90 at the poles. ...

25

Orbits at the altitude of GEO are stable for very long times (millions of years). There is no significant decay of the orbital height due to some kind of drag, so the risk of these satellites interfering with working ones is close to zero. On the other hand, there are good reasons to store them above the belt and not below: The region below is used for ...

25

First you lock on to energy at (or near) the expected frequency. That’s carrier lock. Then you start to look for patterns in how the phase changes. The transmitter is coding groups of bits as phase-change “symbols”, and you want to find the time-pattern of those: symbol lock. But those are not yet bits because the coding works in blocks of bits. Once you ...

23

http://en.wikipedia.org/wiki/Lagrangian_point A satellite orbiting at the L1 point or L2 point would be in constant contact with the moon. Unfortunately, neither of these are particularly useful for keeping in contact with a lunar mission. The L1 point is between the earth and the moon, and would offer no advantages over just putting the reciever on earth....

23

No, quantum mechanics cannot be used to transmit information faster than light. This is a common misconception based on misunderstanding how quantum mechanics works. Go here to read more about it. Technologies like quantum communication are valuable for other reasons though, but they still end up transmitting information at the speed of light, but in a ...

22

Yes, they could theoretically communicate with each other over the DSN, however in practice this will not happen (as it has no current uses). The amount of functions that Curiosity can perform autonomously is very limited and predetermined. It usually involves some sort of deterministic operation such as moving a rover arm or performing a drill sample (...

20

If I understand your edited question, then no. While the Earth's J2 (oblateness) produces enough torque to rotate a Sun-synchronous orbit once a year, it does not produce enough torque to rotate a "Moon-synchronous orbit" once a month. So there is no such orbit. I am not clear on what the utility of such an orbit would be, even if it did exist. If you're ...

20

Actually, it makes a lot of sense to raise the orbit of end-of-life geostationary satellites: Coming from Earth you have to cross through a lower orbit to transfer from low earth orbit to a geostationary orbit but you don't have to go farther out than that (some transfer orbits do, but it's not a requirement). That means that a higher orbit has less risk of ...

20

No. Communication latency (the time between sending a bit and receiving it on the other end) between Earth and Mars probes is limited almost entirely by the speed of light, as they are radio waves on a direct path in vacuum. (There are also plans for optical communications, but as far as I know no Martian orbiter has yet been launched with that capacity. It ...

19

It's not really about tidal effects of the Earth but about irregularities of lunar gravity (Mascons) necessitating large fuel expenditures for maintaining an orbit around the Moon. Taken from: http://boingboing.net/2013/06/23/lunar-gravity-maps.html The solution (first proposed in 1966 by R. Farquhar) is to place a comms relay into a halo orbit around the ...

18

There's already two good answers that say a lot of what I wanted to say, and I will refrain from repeating any of their content here. I do think it is useful to add one more item of insight though. You say: "any quantum switch in this universe can be flipped instantaneously from elsewhere." When people talk about a "quantum switch flipping ...

17

Such satellites are in a geosynchronous orbit (GSO), orbiting at an orbital altitude where orbital period matches Earth's rotation on its axis. Their orbital speed is roughly 3 km/s at mean orbital altitude of 35,786 km above the Earth's surface:    Orbital speeds ($v_o \approx \sqrt{\mu/r}$) at mean altitudes above the Earth's surface (blue) and ...

17

As of today (October 2016), Iridium is the only public satcomm provider using a constellation of low earth orbit satellites with high inclination orbits to provide a service with global coverage. You can compare coverage easily on this website. (this image is from here) Inmarsat and Thuraya in contrast use geostationary satellites, Thuraya uses spot beams ...

17

The experiment has been done, with a single, geosynchronous, satellite, Galaxy IV, in 1998. The immediate effect I noticed in the San Francisco Bay Area was loss of the live NPR feed. I did not check other networks. Second effect, my Chevron Texaco credit card could not be used. The Wikipedia article https://en.wikipedia.org/wiki/Galaxy_IV mentions NPR, ...

16

@Antzi's answer is right, but I'll add some context as a supplement. While Doppler (mentioned there) might or might not be an issue for an off-the-shelf commercial satellite TV box (I don't know) it could probably be fixed with a mod that NASA could easily manage. Several answers to Do astronauts get Netflix on ISS? indicate that there is access to "new ...

15

It is possible in several ways. Let's get the dumb ones out the way first. As I commented, you can orbit the moon itself. Technically correct, since anything orbiting the moon is also orbiting the Earth. You can make your satellite big enough so that it always has a line-of-sight. A giant pole somewhat longer than the Earth's diameter can be arranged to ...

15

The US side of the ISS has a number of antennas to support its rather complicated comm system. Most visible are the two Ku-band High Gain Antennas which are 6 foot diameter azimuth/elevation gimbaled dish antennas mounted on the Z1 truss segment (near the center of the ISS truss). These antennas are sometimes referred to as SGANTs (Space-to-Ground ANTennas)...

15

They are definitely not identical. Tundra is geosynchronous; period = 1 day. The eccentricity allows it to spend most of the time over a region of Earth off the equator, something not possible for geostationary (sit always over one point on equator) or circular geosynchronous orbits (sinusoidal function with slow-down at both extremes). Tundra is intended ...

15

It seems that the company ExoAnalytic Solutions regularly observes high- orbiting satellites (MEO, HEO, and GEO), using the data to provide tracking, ensure they are at the right spot, and provide data in the event of an emergency. They have 200 telescopes dedicated to the effort, which seems to indicate that they can't observe every satellite all the time, ...

14

Satellites in LEO travel at around 7000 m/s. This means that a 1 m sized LEO satellite will take around 150 us (microseconds) to cross a given line between a GEO satellite and a ground antenna. So it is a very short event, and all satellite communications are protected against error bursts (especially from interference) by using FEC (forward error ...

14

Starlink and 5G don't have that much to do with each other--they compete for different customers. Starlink systems currently require a large receiver the size of a pizza box to uplink to satellites. It is unlikely that this will be miniaturized to fit into mobile devices within the next decade or so. 5G is a short-range, high-bandwidth technology designed ...

13

First of all, let's figure out how many satellites per launch vehicle. The estimate of the mass of these satellites is 386 kg. The mass for a launch of a Falcon 9 is 5500 kg. That means one could launch 13-14 satellites per rocket. I suspect 12 is more realistic, because part of the payload mass is the structure to mount all of the satellites, and that is ...

13

I wrote code that flew on 3 spacecraft that went to Mars, one to the Moon, one to a comet and back, and a few Earth-orbiting satellites, the last of which was about 10 yrs ago. All of them used C. It's not the only language out there, of course, but it's popular because the perception is that code can be made smaller and faster using C, without the overhead ...

13

They have to spread their signal. Also, it requires a really big dish to not spread your signal at all. Imagine that there was no spreading at all. The dish would have to be pointed exactly at the satellite, to the margin of the size of the dish. That is far beyond the technology of today! DSS has it's dishes pointed to 0.1 degrees. At the distance of ...

12

Altitude is part of the problem. Assuming you wanted to get to GEO from a circular, 700 km altitude orbit you'd first need to do a burn of about 2.24 km/sec along the orbital velocity direction to raise the apogee of the transfer orbit (the half-ellipse): The spacecraft wouldn't normally do it itself, the launcher upper stage would typically inject you into ...

12

SpaceX has stated a goal that every launch going forward will attempt to land. The expectation initially is not 100% success, but an attempt at the very least. Large GTO payloads do not leave enough fuel reserve for a Return to Launch Site (RTLS) at Landing Zone 1. Instead they will use the ASDS (Autonomous Spaceport Drone Ship) as far downrange as needed ...

11

While power requirements are higher than for regular GSM service, they are not as high as one might think. Current satellite telephones use handsets of the size of 2000-era mobile phones and are able to transmit 15 kBit/s to geosynchronous satellites (the Thuraya system). These satellites are more than 30 times farther from Earth than the planned SpaceX ...

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