# Tag Info

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The Earth's orbital speed around the sun is about 30km/s. Firing a bullet from the vicinity of Earth's frame of motion (e.g. from low Earth orbit) to hit the sun would require cancelling out most of that velocity -- about 25 times the speed of a normal rifle bullet. This might be achievable with a specialized weapon with a very long barrel and a very small ...

42

T-Rex with his tiny brain overlooks the Coriolis force. If the astronaut pointed the gun at the Sun and shot a bullet, it would miss spectacularly. The orbital motion of the Earth makes for a sideward motion of about 30km/s. Depending on how you approach the problem of throwing stuff (radioactive waste and bullets are the same problem) in the Sun, you ...

30

New Horizons went into Earth parking orbit first, so it doesn't count. For a suborbital direct ascent trajectory, some early lunar probes (USSR's Luna-1 for example) would hold this record. Otherwise, early vertical research probes included the Blue Scout Junior, one of which reached 44400 km on 1961 Dec 4 (mission O-2) - another may have reached 225000 km ...

29

This sort of spacecraft is known as a "cycler". You hit on the problem with it: you have to match its trajectory/velocity exactly in order to dock with it, so if you can reach the cycler, you could already reach the cycler's destination. There's no slowing down of the cycler for the same reason. In principle, if you connected to the cycler with a very ...

25

They have shaved off 45 hours, not minutes. It seems to be a whole complex of factors: After the Space Shuttle retirement, the ISS orbit could be raised to provide better ballistic possibilities. The new on-board computer allows to conduct ballistic calculations faster and with less dependence on ground control. The orbit measurements precision has ...

25

The journey to the destination is about always completely pre-planned. All the gravity assists, close fly-bys, and so on, are planned before launch - and often long before the probe design is completed, as often the requirements of the trajectory influence design considerations: ability to hibernate, delta-V of the engines, tolerance to heat if the probe is ...

24

First order analysis Given that we have practical ion thrusters, it's time to look at them. Deep Space 1 The DS1 probe massed 387kg, had 83kg of fuel, operated for 162 days, and generated 92mN. So, it generated about 0.2mm/s^2. The craft is not tanks-dry, either. It has approximately 6 months (180 days) of fuel per design. That's a roughly 20% fuel ...

21

SpaceX published numbers on their website near the bottom of the page. I snapped an image to show here, since their formatting is prettier than I can do in Markdown. You can see that it can do pretty much any of the missions. Now you could probably do a better job with a third stage/kick stage, because while the second stage Merlin-1D Vac has a lot of ...

20

The fastest way to leave the Solar System is to pass by as many of the Gas Giants as you can, and use their gravity to slingshot you faster. As there are no planets outside of the ecliptic, it would not be advantageous to avoid the ecliptic plane. This holds true until we start to get really fast space probes. Furthermore, passing by the planets would give ...

20

In many cases, propellant is only dumped when the spacecraft’s mission is complete, so any minor changes to trajectory caused by the dump are unimportant. If you must avoid any trajectory or attitude change due to a propellant dump, the most straightforward way is to have multiple vents pointing in opposite directions, so the propulsive forces cancel out.

19

According to the plan, an Apollo mission to the moon uses eleven-ish burns. Here are the expected maneuvers: Launch from earth. This you might count as three burns, since it requires all three stages of the Saturn V rocket. They're not only launching from earth at this point, but they're also burning to get into a circular orbit around the earth. Leave ...

19

Altitude drops like that are common when the orbital stage has a high-efficiency, low-thrust engine. It takes a few minutes for the upper stage to bring the craft up to orbital speed. During that period, the craft is indeed starting to fall back towards Earth. The rocket's travel over the curvature of the Earth contributes an effective altitude gain that ...

18

The STEREO satellites used multiple gravitational assists from the Moon to significantly decrease the amount of fuel needed to put those two satellites into heliocentric orbits. The first flyby resulted in STEREO ahead (STEREO-A) being ejected from the Earth-Moon system with a semi-major axis slightly less than that of the Earth-Moon system. STEREO-A has a ...

18

When a spacecraft is launched from Earth, it's moving counterclockwise across your diagram at a speed of 30 km/s (the same speed as Earth itself), plus a speed of 10-15 km/s in the direction of the launch. The trajectory you propose is only possible if you reduce the spacecraft's counterclockwise speed to zero. The fastest launch ever (New Horizons) reached ...

18

It is absolutely possible, just not advised. New Horizons was launched at Solar System Escape Velocity, meaning it could have visited anywhere beyond Earth without stopping. It did visit Jupiter, however, that was to allow it to leave even faster, the Jupiter stop was purely optional. As for the issue of human capable spacecraft, again, it could be done, if ...

18

The asteroid belt isn't nearly as dense as popular media makes it out to be. An answer from the Dawn Mission's FAQ, specifically "What is the average distance between individual asteroids? (6/13/10)", helps here. Asteroids are not distributed uniformly in the asteroid belt, but could be approximated to be evenly spaced in a region from 2.2 AU (1 AU ...

17

The common method for entering GEO orbit is to launch in what is known as a Geosynchronous Transfer Orbit (GTO), which has an apogee at GEO altitude, and a perigee of a few hundred km. Effectively all GEO missions insert their payloads into a GTO (and not into a LEO parking orbit as the OP suggests). There is no benefit of stopping in LEO first, as the only ...

17

Not sure if this counts, but New Horizons was launched directly into an escape trajectory and did not enter orbit. It made it to Pluto and beyond. From Wikipedia: New Horizons was launched from Cape Canaveral Air Force Station directly into an Earth-and-solar escape trajectory with a speed of about 16.26 kilometers per second That might be considered ...

16

Considering that Voyager 1 is already 126 AU from the Sun 36 years since launch, there should be no reason that it would not be possible energetically using a normal launch, small maneuvers, and planetary flybys. Just a Jupiter flyby should be sufficient. Jupiter will also provide the necessary change in inclination. Designing a probe that is assured to ...

16

There are two major reasons you may be going outside the ecliptical plane: You want to get to a particular star. You want to put the Sun on a direct line between your craft and another point in the sky (usually a star system or an interstellar probe to that star system) to exploit Sun's gravitational lens (that is, your destination starts around 550-740 AU ...

15

From the Yellow Book: "06/2022 - Launch by Ariane-5 ECA + EVEE-type Cruise" EVEE means Earth Venus Earth Earth - a long series of gravity assist maneuvers to fit more payload into the Ariane 5 ECA launcher capabilities. Why an Earth slingshot comes first: The fact that the first arc includes an Earth gravity assist for both launch opportunities ...

15

In general, Gravity Assists do not reduce the amount of time, unless you are going really far out there. For instance, Galileo took 6 years to make it to Jupiter after making 3 flybys, one of Venus, two of Earth. Comparatively, New Horizons made it there in just over a year, Voyager 18 months, and Pioneer about 2 years. However, there is considerable fuel ...

15

A gravity assist (or a slingshot) is one of the many compromises in mission design. Instead of going somewhere directly you go somewhere else first and use the momentum of a planetary body to speed up your own movement thus fitting into a Delta-V budget. So the crux of the problem is that gravity assists take time. For unmanned missions, this is acceptable ...

15

The asteroid belt is roughly 6 Astronomical Units wide, and so when it is drawn only 600 pixels wide with each asteroid a handful of pixels wide, you end up with each asteroid being five times bigger than the Sun! I've borrowed a small piece of the image used in @jos' excellent answer to show what I mean. As pointed out in this answer, Wikipedia says: ...

13

Jupiter is 778,500,000 km away from the sun, on average. Earth is 149,600,000 km. Thus, the distance to Jupiter is always between 630-930 million km. So, let's take that range, and figure out what the time would be, given 1 g of acceleration, and ignoring for the moment relativity. Let's also ignore starting/ending velocity, as I'm feeling lazy... Okay, so 1 ...

13

The rule you have for the total $\Delta V$ of a low-thrust spiral is an upper limit arrived at as you let the thrust go to zero. However that takes an infinite amount of time. The total $\Delta V$ of a spiral with non-zero thrust is less, and the time is finite. But it is a good rule of thumb for quick calculations when trying to establish feasibility. ...

13

The minimum $\Delta V$ is effectively a Hohmann transfer. You would de-orbit just enough to barely touch the surface at periapsis, and right at the surface you would do an instantaneous impulsive burn (also known as a "suicide burn") to exactly cancel your velocity relative to the surface. Done! A perfect landing. In the real world however you don't have ...

13

Staying safe (i.e. not falling into the sun) requires an orbit. According to orbital speed of planets, Uranus is the second slowest planet with an orbital speed of 6.81 km/s. This equates to 15,233 miles per hour. Neptune travels around the sun at a speed of 5.43 km/s or 12,146 miles per hour. Although this is a very high rate of speed, Neptune ...

13

Yes, you can shoot the sun with an ordinary rifle and, yes, it would be dangerous. While a typical rifle's muzzle velocity is nowhere near the delta-v needed to hit the sun(Approximately 30 km/s, from low Earth orbit), that is what we have the slingshot maneuver for. Gravity assist is how all of our space probes get anywhere already. So our enterprising ...

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