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70 votes

Have we attempted to experimentally confirm gravitational time dilation?

You don't need a space probe. Or an aircraft. Or even a car. NIST has measured the predicted general relativity time dilation due to a change in altitude on Earth of one foot!
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52 votes

Have we attempted to experimentally confirm gravitational time dilation?

In addition to specific probes like the one mentioned by called2voyage, the effect is significant enough that it affects everyday operations. For example, the GPS constellation needs regular clock ...
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49 votes
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Determining orbital position at a future point in time

Statement of the Problem The problem you want to solve is called the Kepler problem. In your formulation of the problem, you're starting out with the Cartesian orbital state vectors (also called ...
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43 votes
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What does NASA mean when they use the term 'PDT (ERT)'

ERT is Earth Received Time. I.e., when we find out about the event. source
40 votes

Have we attempted to experimentally confirm gravitational time dilation?

Yes, time dilation was experimentally confirmed by Gravity Probe A, launched by NASA on June 18, 1976. The clock rates of two masers (one on the probe and one on Earth) were compared, and it was ...
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30 votes
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How does GPS receiver synchronize time with GPS satellites?

"...the time value received wouldn't be accurate insofar as I know GPS receivers aren't able to determine their position until they've got accurate time." The time value isn't used to tell the ...
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23 votes
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New Year's Celebration on the ISS

The official time zone is GMT, or UTC. As for the number of times they could celebrate, well, that's a bit tricky. The station goes towards the east, which is actually backward in time. There are a ...
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22 votes
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How much faster (or slower) would it be for a new probe to reach Pluto?

Modern technology doesn't change the major constraints of rocket propulsion significantly. In the absence of a gravity assist, the most fuel-efficient route from Earth to Pluto is approximately a ...
21 votes
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How can we transmit a date to another species?

The approach taken by Voyager Golden Record is through use of pulsars. Unlike the insane exponents needed to utilize microscopic physical phenomena or planck time, pulsars operate on ~1 second ...
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21 votes

How do launches avoid leap seconds? Why?

It's not just launches. It's, well, everything. It drives me nuts! Spacecraft flight software almost always have the capability to execute uplinked commands based on time. But what time scale? The ...
  • 65.9k
20 votes

What is the time dilation between Mars and Earth resulting from the mass difference?

From my answer to Parker Solar Probe passing extremely close to the Sun; what relativistic effects will it experience and how large will they be?: From here (or here if you are ambitious) the lowest ...
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18 votes
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Would a Moon resident age differently than someone living on Earth?

The time dilation of the Moon relative to Earth is dominated by not being as deep in the gravitational field of Earth. Not so much the velocity of the Moon. Though the velocity effect isn't ...
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18 votes
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Scott Kelly age vs Twin's

Neil DeGrasse Tyson says that Scott Kelly is now 1/100 second younger than he would have been otherwise, which almost certainly isn't enough to alter the birth order of the two; I don't know which of ...
18 votes
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How do launches avoid leap seconds? Why?

Avoiding leap seconds is easy, don't launch at June 30th or December 31st when a leap second is announced, see https://en.wikipedia.org/wiki/Leap_second It is difficult to test if leap seconds during ...
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17 votes

How does GPS receiver synchronize time with GPS satellites?

To give a big picture view of how the GPS solution is determined, consider the following equation: $\rho_i = \sqrt{(x_i-x_u)^2+(y_i-y_u)^2+(z_i-z_u)^2} +c\Delta t$ where $\rho$ is essentially a ...
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16 votes

What decides if a launch has to be done instantaneously or during a window?

In the case of Falcon 9 / Orbcomm OG2 launch from SLC-40, Cape Canaveral Air Force Station, FL that's now scheduled for Dec. 20th at 8:29 p.m. EST (01:29 a.m. UTC), according to Spaceflight Now: ...
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16 votes

How much light is there on the way from Earth to Proxima Centauri?

No, the power collected by solar panels is reduced by the square of the distance from the light source. At the Earth's distance from the sun, the energy of sunlight is about 1300 watts per square ...
16 votes
Accepted

Is GPS time at least "really close" to TAI (International Atomic Time)?

TL;DR: For all practical purposes except milliarcsecond radio astronomy, TAI and GPS time are separated by exactly 19 seconds. TAI and GPS time both attempt to represent time as ticked by an ideal ...
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16 votes

New Year's Celebration on the ISS

I was interested in the bonus question and decided to do an ad-hoc survey using ISS Tracker in historical mode. I entered the appropriate 2020-01-01 00:00:00 for each apparently relevant time zone (-...
15 votes

How does time work on other planets?

Some basics: Every planet, moon or asteroid have their own rotation period along some specific axis. In very good approximation the period is constant (but not exactly). So every celestial body has ...
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13 votes

The true meaning of Sol regarding time on Mars

From the Wikipedia page on Martian timekeeping: The term sol is used by planetary astronomers to refer to the duration of a solar day on Mars.[7] A mean Martian solar day, or "sol", is 24 ...
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13 votes
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Which Earth time zone most closely matches the ISS astronauts' daily schedule?

The wake/sleep cycle actually does use GMT. It was chosen as a compromise between Moscow time and Houston time. That permits times for meetings between the ISS crew and personnel in either city during ...
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12 votes

If the Alcubierre Warp Drive was used to travel to Alpha Centauri, how much time would pass on Earth?

The Alcubierre bubble could get to Alpha Centauri in less than 4 years according to outside observers, not just observers riding inside the bubble--the exact time depends on the exact 'shape' of the ...
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12 votes
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Where can the term "Sol" used?

A "sol" is only commonly used for a Martian day, and it seems pretty redundant to use this term for Earth, as it is already covered by the concept 'day'. Also, it may induce ambiguity, as people think ...
12 votes
Accepted

How are GPS satellite clocks synchronized with each other in the earth's frame of reference?

The satellites' location is very accurately determined using ranging techniques, where a pulse is sent from a ground station to the satellite and the satellite responds very quickly, with a known time ...
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12 votes
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What kind of time regiment/schedule do ISS astronauts have?

Like a lot of things that should be readily available, it's frustratingly difficult to find this on any NASA web site. Fortunately ESA came to the rescue in the form of a blog post about Alexander ...
12 votes

Apollo Missions - Travel time to moon

Escape velocity is the velocity at a given altitude (usually the surface) that is enough to leave the body's sphere of influence with a positive net velocity. But if you leave a body at exactly escape ...
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11 votes

How much faster (or slower) would it be for a new probe to reach Pluto?

For a launch to Pluto, a Jupiter gravitational slingshot opportunity occurs once every 12 years or so (one Jupiter orbit + 12/248, to account for Pluto's movement in those 12 years). The next one is ~...
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11 votes

How to obtain UTC of the epoch time in a satellite TLE (two line element)?

The best guess available about the time scale used in TLE files is from the epic Revisiting Spacetrack Report #3 report from Celestrak, which they have put online here: http://www.celestrak.com/...
11 votes
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How far from earth have atomic clocks (or ultra-stable oscillators) been placed and monitored?

There was Rb-based Ultra Stable Oscillator in outer space, delivered to Titan (VI moon of Saturn) inside the Huygens, brought there by Cassini. (DWE RUSO in http://nssdc.gsfc.nasa.gov/image/spacecraft/...
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