Hot answers tagged

211

To be honest, I don't know how to measure atmospheric pressure, so I cannot discriminate on that basis. Initially my answer only included unmanned missions, but based on suggestions I've decided to add the Apollo missions as well. Moon The first landers performed intentionally hard landings and did not get pictures from the surface. I want to include them ...


102

Very good question! The answer boils down to statistics of failure. Some aspects involve the statistics of "random" failures—for some reason some critical component just bites the dust—and some involve event-driven failures, such as failures induced by landing shocks, long engine burns, atmospheric entry stresses, etc. When someone (a government, usually) ...


82

New Horizons will never overtake Voyager 1. Although New Horizons is currently faster than any other man-made object, it won't be by the time it reaches the outer corners of the solar system. From the John Hopkins University/Applied Physics Laboratory New Horizons page: Though New Horizons will also reach 100 AU, it will never pass Voyager 1, because ...


67

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!


59

I think a lot of folks see these gorgeous photos of distant galaxies, with fine detail on dust lanes and spiral arms and assume that since they’re so far away, seeing Pluto would be easy. But while these galaxies are far away, they’re also huge. The (relative) detail that can be seen in any given telescope will be found by the object’s size divided by the ...


57

Tardigrades can survive vacuum, low temperatures, and moderate radiation for quite a while. They're multicelled organisms. How tough is the toughest hypothetically viable single-celled extremophile? How sure are you that we've found all of them on Earth already? It's a matter of caution. Contamination of another planet (or moon) is likely to be irreversible,...


51

Starting out from Earth, you have the free 30 km/s from Earth's movement around the Sun, which is in the plane of the ecliptic. To get far out of the plane you either have to boost a similar amount "up" or "down" (which is beyond the capability of current rockets) or go via one of the gas giants, and use its gravity to change course. So at least to start ...


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 ...


50

The main reason for using tantalum is the fact that it is a rare element. When they capture the debris thrown up by the bullet, the fact that the bullet itself is tantalum makes it easy to distinguish it from the asteroid's material. If they used a more common element like iron, scientists could not be sure that any iron was from the asteroid, instead of ...


49

The trajectory was not only "unhindered" - it was enhanced! Knowing mass of the planet you can calculate very precisely how the trajectory of a probe flying by will be affected. You modify the trajectory on arrival in such a way, that the departure trajectory will be exactly as desired. And due to some rather unintuitive physics caveats, you can make it so ...


48

There are a lot of generic answers here about spacecraft. I will try to answer the question specifically for Spirit and Opportunity. 90 sols was deemed sufficient to conduct the primary mission of the rovers, so the systems were designed and tested to assure full capability through the entire 90 sols. The first thing expected to take a rover below full ...


47

Preface: I am far, far from an expert in space electronics; I don't think I can weigh in on how much these sensors actually are, which is the title question; all I can offer is an uneducated inane ramble on where that money might be going. Let's take your analogy of a bargain-basement thermal sensor; actually, let's specify a common off the shelf Melexis ...


47

The teeth served an aerodynamic function. ...metal teeth were added to the periphery of the impact ring in an effort to reduce the spin and oscillation during the descent and prevent the rough landings experienced by the 1978 missions. This is also why the earlier missions didn't have them, they were added in an attempt to mitigate problems experienced on ...


46

Here's a nice graph of Voyager 2's speed, and the difference made by the gravitational assists: You can see that the probe slowed down between assists. New Horizons would follow a similar graph, but with fewer assists its speed will end up below Voyager 2's, as @gerrit said.


43

When will we send? We already did. In 1985 and 1986 the Soviet Union sent two Vega probes to Venus. Both included a robotic balloon (usually called aerobots). The two balloon aerobots were designed to float at 54 km from the surface, in the most active layer of the Venusian cloud system. The instrument pack had enough battery power for sixty hours of ...


41

First a few terms: Low Earth Orbit (LEO) All spacecraft must first achieve low Earth orbit. This is true whether you're sending stuff to the Moon or Mars. Trans Mars Insertion (TMI) The burn needed to send something on its way to Mars. Delta-v Change in velocity needed. Usually measured in kilometers/second. An important metric for space missions. Earth ...


40

Distance. Size of the target. Its poor albedo at such distance to its only source of illumination, the Sun, compared to closer celestial bodies. And movement of the target and the vantage point in their orbits preventing advanced image interpolation techniques combining multiple observations of same side of Pluto at same lighting conditions. Pluto is ...


39

We've had 5 flyby missions to the outer solar system so far. All of them had primary missions at one or more planets. That set the main constraints for their trajectories. Anything after the last planetary encounter was secondary. For Voyager 2, for instance, the Neptune flyby was aimed at a close encounter with Triton, which reduced the possible exit ...


38

From the Voyager FAQ Question: Can the Voyager imaging cameras be turned back on? Answer: It is possible for the cameras to be turned on, but it is not a priority for Voyager's Interstellar Mission. After Voyager 1 took its last image (the "Solar System Family Portrait" in 1990), the cameras were turned off to save power and memory for the ...


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 ...


38

I'm showing the calculations for Russell Borogove's excellent answer. You've asked to accelerate an object to 0.1 times the speed of light. Mathematically, $$\left( \frac{\Delta v}{c} \right) = 0.1$$ The exhaust velocity $v_e$ of an ion thruster is 20-50 km/s. Let's pick $v_e=30,000 \text{ m/s}$, thus $$\left( \frac{v_e}{c} \right) = 10^{-4}$$ And let's ...


37

Any hypothetical planet (or other object) even further out would be very dark, so few photos are taken for any reason other than to look inward. (And in any case, the cameras on the Voyagers are shut down due to lack of power.) So discovery by camera would be very unlikely. What would trigger a discovery would be deviation of trajectories from those ...


35

This mission study came up with a 900 kg nuclear-electric-propulsion spacecraft launched on an Ariane V with a C3 of 100 and a Jupiter gravity assist along the way. 1.05 kW electrical power at Pluto from RTGs is required. That would be four "classic" NASA RTGs, or about nine MMRTGs. It has a 20 kg science payload. (New Horizons has ~30 kg of instruments, ...


35

No. 10% of the speed of light is about 30,000,000 m/s. Our fastest space probe to date, New Horizons, left Earth at less than 1/1000 of that speed. With a large propellant tank and a high-efficiency ion thruster we could reach something like 300,000 m/s, about a tenth of 1% of the speed of light. Due to the exponential nature of the rocket equation, ...


33

Why are people so fascinated about Mars and not about Venus at all? The trivial answer - Mars is moderate place. A human could easily get around with a spacesuit, and it is trivial for robots and equipment to exist on Mars. Venus is a swirling hell. The "atmosphere" is a sea of incredibly hot, ultra-boiling, 800+ F° sulfuric acid (!!!) (Indeed, Venus is ...


32

Voyagers are still active, and albeit they don't have the power required to run all the scientific equipment onboard and some of it stopped working by now, they still transmit telemetry data streams towards the Earth that is picked up by NASA JPL's 70-meter antenna at Goldstone, California, part of the Deep Space Network. Quoting from Wikipedia on Voyager ...


29

No, it's not feasible. The fundamental problems that prevent this are: The Pioneers do not have enough power to operate the transmitter, due to corrosion of the thermocouples The Voyagers and Pioneers, even at full power, use very low power transmissions The Pioneers would need to be able to receive and obey instructions to aim for a Voyager The craft are ...


29

No, not yet. The Parker Solar Probe became the closest ever artificial object to the sun on October 29th, 2018, surpassing Helios 2 which held the record since 1975 [1]. No other human-made object has been closer to the Sun. The probe will repeatedly touch the outer corona until mission end in 2025, with the closest approach being 3.83 million miles [2]. It ...


28

Space is basically a vacuum, so there's no air resistance. A probe that's been launched will travel at the same speed indefinitely. Because New Horizons is moving away from the Sun, it loses some speed to overcome the Sun's gravity. New Horizons was launched on the fastest rocket they could get. Then it used a gravity assist from Jupiter to gain some more ...


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