71
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....
- 128k
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 ...
- 122k
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 ...
- 188k
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 ...
- 128k
38
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 ...
- 170k
38
votes
If a sitting President went to space on a USSF spacecraft, would the call sign be Space Force One?
This FAA doc for air traffic control processes on page 2-4-9 says
When the President is aboard a military
aircraft, state the name of the military service,
followed by the word “One.”
And followed ...
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30
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:
...
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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 ...
- 48.2k
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....
- 170k
27
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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25
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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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 ...
- 149k
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 ...
- 149k
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 ...
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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 ...
- 4,578
21
votes
Accepted
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
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 ...
- 20.3k
20
votes
Accepted
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
(...
- 188k
19
votes
Accepted
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 ...
- 149k
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 ...
- 291
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 ...
- 2,506
18
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 ...
- 5,311
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 ...
- 170k
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 ...
- 128k
15
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 ...
- 48.2k
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 ...
- 122k
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
...
- 188k
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 ...
- 7,226
13
votes
Accepted
How will the closure of the Arecibo dish impact deep space communications?
There is some indirect evidence that Arecibo's loss has already impacted communication with some of the deep space probes.
NASA's official statement on Arecibo says this:
NASA’s Goldstone Observatory ...
- 48.2k
13
votes
Have solid dish antennas on deep space spacecraft (as opposed to meshes) ever provided any other helpful function? As meteor shields perhaps?
A few months before Cassini made its mission-ending dive into Saturn's atmosphere, it skirted the region between Saturn's atmosphere and the innermost ring.
From NASA Spacecraft Dives Between Saturn ...
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