72 votes

How did NASA prevent third parties from spoofing Apollo communications?

The signal from the Moon was received using giant parabolic antennas, e.g. the 64-m dish at the Parkes observatory. These have very good sidelobe rejection so they won't pick up any Earthbound signals....
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62 votes

Why would GPS availability be reduced by high demand (or solar eclipse)?

GPS isn't affected by demand, as it is transmitting only from satellites, and the receivers only receive, they do no transmit to the satellite at all. At best, there is a slight degradation by having ...
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45 votes

Has any spacecraft ever had the ability to directly communicate with civilian air traffic control?

Yes. The space shuttle could. I recall in shuttle ascent abort training, when the crew was executing an East Coast Abort Landing to an airbase / airport on the East Coast, the commander would ...
39 votes

Why would GPS availability be reduced by high demand (or solar eclipse)?

As PearsonArtPhoto says, it's not the GPS protocol itself that causes the problem. Cell phones use Assisted GPS, where cellular data is used to speed up obtaining a GPS fix. This should be just a ...
  • 122k
39 votes

Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

He replied that we actually received the signals in just 1-2 seconds with the help of MarCO CubeSats. Later on followed up with confusion from other users with his statement and asked for ...
31 votes

Apollo communication between the Earth and Moon

It can be seen through this Wikipedia article that all communication with the Apollo missions was done at about 2.2 GHz, which is well above the frequency that reflects on the Ionosphere (No higher ...
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29 votes
Accepted

Has any spacecraft ever had the ability to directly communicate with civilian air traffic control?

Yes. The Soyuz Escape Capsule Responding Instructions explicitly document 121.5 MHz capability, including voice: ...
29 votes
Accepted

Why did Moon missions state their number in radio context?

The standard protocol for any radio communication is to specify the intended recipient and the transmitter's call sign. This practice started in the earliest days of radio. Stations were sharing a ...
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28 votes
Accepted

Did USSR discontinue radio transmissions, relocate ships, to aid the US in response to Apollo 13?

According to NASA's Space Educator's Handbook: As the men in Apollo 13 experienced what no men had undergone before, millions followed the developing drama by radio and television in public squares, ...
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28 votes
Accepted

Was "I have the farts, again" broadcast from the Moon to the whole world?

It depends on what you mean by "broadcast to the whole world". According to the annotated transcript (h/t to Organic Marble for finding it) John Young said it into a "hot mike", i....
26 votes
Accepted

Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

Apparently not: I like this Quora answer. Here's part of it, the rest is worth reading as well: No experiment conducted using entangled photons has ever demonstrated faster than light communication! ...
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26 votes
Accepted

What is carrier lock and bit lock?

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-...
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24 votes

How did NASA prevent third parties from spoofing Apollo communications?

The difference between 10 W at 350,000km, and 1,000 W at 1km is 131 dB. If the pranksters on Earth used a directional antenna like the Ham radio operators shown below, the ratio would be even higher ...
  • 148k
24 votes

Why not send Voyager 3 and 4 following up the paths taken by Voyager 1 and 2 to re-transmit signals of later as they fly away from Earth?

It's a great question! Trajectory To get a few decades more out of them, you can launch Voyagers 3 and 4 sometime around now and get by with a maximally-boosting flyby of Jupiter since you wouldn't ...
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23 votes
Accepted

What happened to Voyager 2's tracking loop capacitor? How did it get damaged? What is it for? What's a tracking loop anyway?

On April 6, 1978, a fault-protection algorithm onboard Voyager 2 automatically switched from the prime to backup receiver. However, the backup receiver's tracking-loop capacitor3 was found to have ...
22 votes
Accepted

Would adding satellites between Earth and Mars improve communications latency?

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 ...
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21 votes
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Tracking of spacecrafts of the Mercury project

NASA report SP-6, chapter 2 describes the tracking network in detail. It provides this overview schematic explaining how the various stations communicated with each other: (source: NASA SP-6, chapter ...
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20 votes
Accepted

How much RF transmit power does DSN need to send commands to Voyager?

Check the DSN Now page when it will show any of its stations communicating with Voyager 1 (code VGR1) or Voyager 2 (VGR2), select that dish and then expand the side column on the right to show all the ...
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20 votes

Why not send Voyager 3 and 4 following up the paths taken by Voyager 1 and 2 to re-transmit signals of later as they fly away from Earth?

You have a few problems with doing that which @uhoh unit has already elaborated. Even if you could surmount those you have a bigger problem, which is the Voyager probes will have to shut down their ...
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19 votes

Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

As someone deeply involved in quantum information/entanglement research: You cannot, under any circumstance, use entanglement to communicate faster than lightspeed. Ever. The "no-signalling ...
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19 votes
Accepted

Why was Canberra able to listen to Voyager 2 but not talk to it?

As per the March 4 JPL News story, only DSS43 has the right S-band transmitter, enough power and is in the right hemisphere to talk to Voyager: Moreover, a special S-band transmitter is required to ...
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19 votes
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What kind of signals and encodings were used to send tilt/pan commands to TV cameras on the Moon (up through Apollo)?

For the Ground-Commanded Television Assembly (GCTA) mounted on the rover that was used to image Apollo liftoffs from the moon: The real-time command messages consist of three vehicle address bits (...
18 votes
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How to calculate data rate of Voyager 1?

OK let's first understand units. The decibel (dB) is a base-10 log scale without units and dBm is a similar decibel scale for power referenced to 1 milliwatt. They also include a factor of 10, so for ...
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17 votes

Why did Moon missions state their number in radio context?

In addition to DrSheldon’s points, it’s worth noting that the communications between Houston and the spacecraft are only one part of what each controller in mission control is hearing. Rather than ...
16 votes
Accepted

Deep Space Network time budgets per spacecraft - is such statistics available?

I submitted a FOIA request for every contact made by the DSN from 2010 onward (I received contacts from Jan 1, 2010, till Sep 1, 2018) Here is a summary of the contact time for all 86 Missions ...
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15 votes

Are and should satellites use wireless communication internally, rather than cables?

Radio may reduce some complexity, but it will introduce problems that wiring doesn't have. Limited bandwidth. Interference. You can separate wiring so it doesn't influence each other. Can't do ...
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14 votes
Accepted

Do satellite uplink/downlink signals spread or leak into space?

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 ...
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14 votes
Accepted

Why have four parabolas on a ground-side array instead of just a single large one

It's a very simple phased array antenna. Other examples include cell phone antennas, this French satellite tracking antenna, and the famous Very Large Array (VLA) in New Mexico. You create a ...
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14 votes

Encryption in radio system

At least for the Space Shuttle, commands to the orbiter from the ground were routinely encrypted. Communications Security Communications security (COMSEC) equipment provides the capability ...
13 votes
Accepted

Would an orbital Deep Space Network be more efficient?

Let's think about what it would take to do what you're suggesting. The DSN uses some pretty large antennas, so you're talking about putting a 70 meter dish like this (and a power supply to run it) in ...
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