# Tag Info

26

You can't do it. It's impossible. Each thruster provides thrust, but each thruster has mass, as do the power sources needed to power them and the tanks to store their fuel. No currently existing ion thruster is able to produce anywhere near that much thrust for its mass, and more significantly, even the best power sources (even speculative ones or those at ...

16

Ion engines balance two different kinds of efficiency: $I_{sp}$ which is basically "reaction mass efficiency". For that you want the highest possible exhaust velocity, which will be helped by a higher voltage. Energy efficiency for which you want the exhaust velocity to be in the same range as the $\Delta v$ required for your mission. With a given ...

11

Knowing that the thrust is proportional to the grid voltage Almost correct! All else equal, the thrust will be proportional to the ion velocity, which will vary as the square root of their kinetic energy, which is proportional to the acceleration voltage. why don't they just eject some electrons from the grid to increase the electrical potential? Well to ...

10

This is a great question! To first order charging doesn't matter. What matters is the exit velocity of the ions, determined by the acceleration potential difference $V_b$. In a simple situation the thrust is the velocity of the ions with respect to the spacecraft times the mass flow rate $dm/dt$ of the ions, and that velocity is determined by (something like)...

8

Probably not. To control the point of reentry, you need to be able to adjust from a perigee high enough to not promptly reenter (i.e. above 200km) to one low enough to promptly reenter (i.e. below 80km) in significantly less than the time it takes to complete a single orbit -- otherwise, the unpredictable effects of drag in the variable density upper ...

8

If you increase the grid voltage of an ion thruster, you need more, bigger and heavier isolation to avoid arcs and current flowing thru the isolation. The thruster gets much bigger and heavier, the reliability is lower. When thrust to weight ratio gets worse there is no benefit of higher voltage. To generate large DC voltages for the thruster you have to ...

7

I don't have an exact GTO-to-GEO transfer on hand, but I have this figure from a class assignment from a few years back. While definitely not a practical trajectory, it shows the characteristics of how to transfer from an elliptical to a circular orbit. This solution was computed using indirect optimization. This problem assumed constant thrust magnitude (...

5

Other than the Star Trek one, these images are of the controls of the JPL 25-foot space simulator. This was built in 1961 which is why it looks like it does. It is still in use, and Ingenuity, for instance, was tested in this. Here is a blog post from someone who visited it: you can see an image of part of the control panel there. I'm afraid I don't know ...

4

You're right that one of the main objective is to remove charge from the satellite to keep it neutral (to avoid ions returning to the satellite). But, and here comes the important point: You calculated that the ions just reach escape velocity. That means, when approaching infinite distance, their speed approaches zero! And, with the ions being at rest with ...

4

No, that's impossible. You can't compress an ionized gas and put it into a cylinder like that. All familiar ordinary matter, including gases, is not ionized, or else only slightly ionized. If you try to squish a large amount of ionized oxygen atoms together to reach a dense gas, let alone a super-compressed one, the following will happen: The oxygen will be ...

2

I think there is a bit of confusion in the terms people use for iodine in the space propulsion community. For more detailed information I recommend having a look in one of these scientific articles Dietz et al. (2019) and Szabo et al. (2013). I will base my answers on them. Iodine is not used in solid state for electric propulsion (EP). People like to use ...

2

I originally posted this answer here. This is a figure that I have from a class assignment from a few years back. While definitely not a practical trajectory, it shows the characteristics of how to transfer from an elliptical to a circular orbit. This solution was computed using indirect optimization. This problem assumed constant thrust magnitude (so the ...

2

It is always important to keep the charge of a spacecraft close to zero and to never get too large. This is true no matter if you are using ion propulsion or not. A charged spacecraft can suffer from several failure modes. So when a spacecraft emits positive ions it also must use an electron gun to emit electrons to keep the spacecraft close to neutral. ...

2

You can get a very approximate answer just from fundamental physics. Your ions probably have $e$ unit of charge (ie they are missing one electron), so in dropping through a potential $V$ Volts they will acquire $Ve$ Joules of energy. So if they have mass $m$ and exhaust velocity $v$ you will get $$\frac{1}2 mv^2 = Ve,$$ so $$v = \sqrt{\frac{2Ve}m}$$ Now ...

2

You have come up with a good list of possibilities. Some see this as relatively straightforward, including me, though manufacturer marketing may cloud the issue. Any kind of electrical augmentation, such as resistor jets or hydrazine arcjets, should count as electric propulsion because the satellite manufacturer has to factor in the power needed over and ...

2

I suspect that what you suspect is the problem is actually the answer. MEV is intended to dock with spacecraft that were not intended to dock with, and control the orientation of those spacecraft. Therefore, there are a number of situations that it has to deal with, where the center of mass will be different. It has to control that center of mass when it is ...

1

If the MEV could adjust orientation traditionally, with reaction wheels, then no advantage is gained by applying thrust in a line that doesn't pass near the craft's center of mass. But as far as I can tell, the MEV eschews reaction wheels because its mission is to repair satellites whose wheels have failed. Even if the failed ones are decades older, ...

1

There are a lot of ions in space already, adding a few from the thruster is not really that big of a deal. They are moving so fast that it won't really make a huge difference being neutral or not, they are going away from the spacecraft, and at the point where electrons are typically injected they are far enough away that it doesn't matter much. All that ...

1

The Problem you are assuming, is actually none: Temporarily stored electrons are finally reinjected by a neutralizer in the cloud of ions after it has passed through the electrostatic grid, so the gas becomes neutral again and can freely disperse in space without any further electrical interaction with the thruster. Source: Ion Thruster Wiki, just in the ...

1

Would this engine produce any thrust? Yes, but not in the way you envision. Ice in a vacuum sublimates to steam, which will create a tiny bit of pressure (on the order of a few Pascals, barely enough to even measure). As the steam escapes down the tube and out into space, it will produce a slight thrust in the opposite direction. The fact that the sun is ...

1

Apparently they aren't even restricted to noble elements: This great paper from AFRL notes that bismuth is a good contender that has been demonstrated in Hall thrusters. The drawback with fuels that are not gases at very low temperatures is that: They have to be vaporized, which requires extra energy and engineering. If they are not gaseous at low ...

1

I think the term is used like it is with automobiles. According to Wikipedia's hybrid electric vehicle page they don't have to operate together to be a hybrid (at least for autos). I would think that keeping the trusty R-4D, see Wikipedia's "Used In", adds the some all important reliability to the system.

1

Cerres orbital speed is 17km/sec To make it intercept, you need to do a 5km/sec burn according to http://www.projectrho.com/public_html/rocket/appmissiontable.php Cerres is 9x10^20kg In other words you need to make Cerres lose 1x10^30J Of course, we should reduce that number because you’re using the mass of Ceres itself as reaction mass. Since you propose ...

1

OKEANOS was a JAXA project of circa 2010, combining a solar sail and an ion engine. Authors were going to send it to Jupiter's trojan asteroids with a possible sample-return trip to Earth. The sail would have been made of a 10 μm-thick polyimide film measuring 40 × 40 meters (1,600 $m^2$) covered with 30,000 solar panels 25 μm thick, capable of generating ...

1

Unit of impulse is newton-sec and not newton/sec and it is not equal to thrust because you are not going to accelerate all the ions in duration of 1 sec. Therefore, if it takes more than 1 sec then your thrust would be lesser than your calculated impulse value.

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