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68

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!


50

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 corrections because the satellite hardware sits much higher up the gravity well than the ground hardware. The Wikipedia page for gravitational time dilation ...


44

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


38

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 Cartesian elements): that is, the initial position and velocity. As you have discovered, the only way to propagate the Cartesian elements forward in time is by ...


38

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 found that the difference matched what was predicted with an accuracy of about 70 parts per million. To address your question of challenges in designing the ...


23

"...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 receiver what time it is (at least not directly, although that is helpful later). It's used so that the receiver can tell relatively what the distance is to each ...


22

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 45-year journey. Bringing that down to 9 years already represents a large investment in propulsion fuel; New Horizons set the record for the highest launch speed ...


21

Like many armed forces, and Stack Exchange, they use UTC (or Zulu time) Historically, Greenwich Mean Time was accepted as being the definitive time zone in 1884 to aid navigation (which then, as now, relied on accurate time) - and the Prime Meridian was defined as running through Greenwich at 0 degrees Longitude. Coordinated Universal Time (UTC) succeeded ...


21

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 timescale, which makes them quite convenient. A map specifiying location of Earth in relation to a number of pulsars identified through ratios between their ...


18

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 the two was born first.


16

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 range from the user to the GPS satellite, $x,y,z$ are position coordinates, the subscript $i$ indicates the particular satellite, $c$ is the speed of light, and $\...


16

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 meter, of which something like ~30% can be converted to electricity by solar panels. Once the sun is far enough away to be "just another star", the total ...


14

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 negligible, being about two orders of magnitude down from the gravity effect. Time passes about 0.66 parts per billion faster on the Moon than on Earth, due to not ...


14

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: Sources said only an instantaneous launch opportunity is available Sunday due to restrictions imposed by the Federal Aviation Administration, which may be ...


14

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 clock at mean sea level on the surface of the Earth. Both differ from UT1, time as ticked by the Earth's rotation (this is the source of leap seconds), and ...


13

According to JPL's Voyager FAQ: There is no clock chip, as such, in the spacecraft. The "clock" is really a counter, based on one of several electronically generated frequencies. These frequencies, based on a reference, generated by a very stable oscillator, are converted and fed to different locations in the spacecraft as synchronization signals, ...


13

While it is true that just about everything uses UTC on the ISS, the crew's schedule moves around. For example, if there is an upcoming EVA that must be done at a particular time, or a spacecraft arrival/departure scheduled, ground control will adjust the sleep cycle of the crew over several days. Thus the "day" as defined on the station by when the crew ...


13

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 some of their normal working hours.


12

Virtually all spacecraft use one of two time conventions, or more likely, both of these Universal Time Coordination (UTC) GPS Time The difference between these two is slight, but changes periodically. The difference is currently 16 seconds, as can be seen on this clock. The reason for the difference is the failure for GPS time to keep track of leap seconds ...


12

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 hours, 39 minutes, and 35.244 seconds.[6] “Sol” is often used as a direct replacement for “Day” when concerning Mars. Mission duration for Mars missions is ...


12

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 warped spacetime in the bubble, but the theory allows you to fine-tune the bubble to give as short a time as desired. The fact that observers outside the bubble ...


12

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 between receive/transmit. This allows one to determine exactly how far away the satellite is. Combining this information with orbital tracks allows one to ...


12

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 velocity, your velocity bleeds off as you climb in exchange for gaining gravitational potential energy, and your velocity tends to the limit of zero at ...


11

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 ~2-3 years away. Then there's the rocket. You want the fastest launch possible. The Atlas V 551 used by New Horizons can put 18 tons into LEO. As a first ...


11

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 you are referring to a Martian day. As for the other planets in the inner solar system, Mercury and Venus, they have a so long day that their orbital period ...


10

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/huygens_cutaway.jpg). Schemes and paper - RUBIDIUM ULTRA-STABLE OSCILLATORS AT TITAN: THE HUYGENS DOPPLER WIND EXPERIMENT, 1997. THE HUYGENS DOPPLER WIND ...


10

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 order terms to the relativistic frequency shift of a clock in orbit around a gravitational body are: $$ \frac{\Delta f}{f} \approx -\frac{\Phi}{c^2} - \...


9

The problem The GPS receiver's time has to be synchronized with atomic clocks located in GPS satellites. It is kinda chicken or the egg problem. The receiver needs precise time to calculate precise distance and precise distance to synchronize time (to calculate the time difference). The answer It is the fourth satellite that gives your receiver the ...


9

Assuming you are talking about a 'classic' launch, one with rockets pushing something into orbit, no - it's completely irrelevant. Darkness? Bah. Space programs have enough lights to send darkness cowering away in a corner, just like football games. Ultimately, it's all about ballistics (the physics of getting from point A to point B). If the space ...


9

Was that option considered in detail? Almost certainly not. This question is based on the false assumption that staffing levels remain more or less constant across all phases of flight. This is not the case. Staffing is very light during passive phases such as coast. Requirements for communications mandate a large antenna. No matter how good we become at ...


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