5/23/2023 0 Comments A space in time song bookThey compute a best-fit trajectory that, for a Mars orbiter, is typically accurate to within 10 meters (about the length of a school bus). The distance and speed measurements are collected by the ground stations and sent to teams of navigators who process the data using sophisticated computer models of spacecraft motion. Likewise, the clocks’ contribution to error in the orbiter’s speed measurement is a minuscule fraction of the overall error (1 micrometer/sec out of the 0.1 mm/sec total). DSAC’s resulting stability is on par with ground-based atomic clocks, gaining or losing less than a microsecond per decade.Ĭontinuing with the Mars orbiter example, ground-based atomic clocks at the Deep Space Network error contribution to the orbiter’s two-way light time measurement is on the order of picoseconds, contributing only fractions of a meter to the overall distance error. DSAC uses this property to measure the error in a quartz clock’s “tick rate,” and, with this measurement, “steers” it towards a stable rate. The precision of the Deep Space Atomic Clock relies on an inherent property of mercury ions – they transition between neighboring energy levels at a frequency of exactly 40.5073479968 GHz. The result is a clock system that can be ultra stable over decades. By measuring very stable and precise frequencies of light emitted by certain atoms (examples include hydrogen, cesium, rubidium and, for DSAC, mercury), an atomic clock can regulate the time kept by a more traditional mechanical (quartz crystal) clock. Measuring time, way beyond Swiss precisionįundamental to these precise measurements are atomic clocks. We collect the distance and relative speed data over time, and when we have a sufficient amount (for a Mars orbiter this is typically two days) we can determine the satellite’s trajectory. We can measure the travel time of the signal and then relate it to the total distance traversed between the Earth tracking antenna and the orbiter to better than a meter, and the orbiter’s relative speed with respect to the antenna to within 0.1 mm/sec. The time the radio signal takes to travel there and back (called its two-way light time) is about 28 minutes. Then, from how long our “two-way” measurement takes to go there and back, we can compute distances and relative speeds for the spacecraft.įor instance, an orbiting satellite at Mars is an average of 250 million kilometers from Earth. We know the signal is traveling at the speed of light, a constant at approximately 300,000 km/sec (186,000 miles/sec). The Canberra Deep Space Communications Complex in Australia is part of NASA’s Deep Space Network, receiving and sending radio signals to and from spacecraft. To navigate in deep space, we measure the transit time of a radio signal traveling back and forth between a spacecraft and one of our transmitting antennae on Earth (usually one of NASA’s Deep Space Network complexes located in Goldstone, California Madrid, Spain or Canberra, Australia). Our goal is to develop an advanced prototype of DSAC and operate it in space for one year, demonstrating its use for future deep space exploration. In its final form, the Deep Space Atomic Clock will be suitable for operations in the solar system well beyond Earth orbit. It will improve accuracy and enable new modes of navigation, such as unattended or autonomous. DSAC is a small atomic clock that could be used as part of a spacecraft navigation system. But to actually do it we need better tools – much better tools.Īt NASA’s Jet Propulsion Laboratory, I’m working to develop one of these tools: the Deep Space Atomic Clock, or DSAC for short. In school we learned that speed and time will tell us how far we went in traveling from point A to point B with a map we can pick the most efficient route – simple.īut what if point A is the Earth, and point B is Mars – is it still that simple? Conceptually, yes. We also use time to navigate our way to the destinations that matter to us. Every day we count its passage and use it to schedule our lives. We all intuitively understand the basics of time. DSAC is prepping for a yearlong experiment to characterize and test its suitability for use in future deep space exploration.
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