Comments on: NASA will fly a test drone on 2020 Mars rover mission

By: Edward

Edward — Tue, 15 May 2018 22:45:25 +0000

Localfluff asked: “Why would hydrogen leak less than helium?”

Max answered: “He meant that helium would leak out slower than hydrogen.”

Helium is atomic and hydrogen is molecular. The tiny helium atom permeates materials relatively easily but the larger hydrogen molecule not so much.

Vacuum chamber operators use helium to check for leaks, because it fairly easily goes through the tiniest of holes or cracks or past scratches in seals. However, when (synthetic) rubber seals are used, the helium permeates into the seal and slowly comes out, making looking for leaks around such seals troublesome and time consuming, but helium is still used because a leak will make itself known quickly, once the operator eventually gets to where the leak is occurring.

For the same reasons, helium will escape from balloons faster than hydrogen.

Hydrogen is generally thought to be more dangerous, but that is because of the oxygen in Earth’s atmosphere. Mars has a CO2 atmosphere, so a hydrogen balloon there would not be as much of an explosive hazard as on Earth.

By: Max

Max — Tue, 15 May 2018 14:25:55 +0000

He meant that helium would leak out slower than hydrogen. Hydrogen has an atomic number of 1, helium is 2. But helium has two neutrons and two protons which makes its atomic weight 4 times that of hydrogen. (It’s a wonder that the helium doesn’t snuff out the Sun’s core, choking on its own byproduct)
Hydrogen definitely provides more lift, but there is no container that can hold it for very long because the atoms are so small that it passes right through. I believe the losses are 10% per day, that’s why hydrogen tanks are double walled. What leaks through to the inner compartment is pumped back into the tank.
The cold war space would keep hydrogen loss to a minimum but it would still be a problem. For a balloon to use Hydrogen it would need to create it upon need. electrolyzing water, or lye and aluminum.
Helium can be kept in a light metal container with a microvalve controlled by altitude and could last years. A dirigible could have propellers to steer it.

Edward wrote;
“I am a little concerned that it may tip over on landing. Can it right itself?”

If the helicopters propellers touch the ground while turning at high speed, it is likely that it will not do so without damage. The action/reaction of the blades against the ground or rock will provide more thrust then the blades spinning in the air. In other words, it’ll ricochet off anything it touches launching itself in the light gravity tumbling end over end.

By: Localfluff

Localfluff — Mon, 14 May 2018 03:39:27 +0000

@Edward
Why would hydrogen leak less than helium?

By: Edward

Edward — Sun, 13 May 2018 23:53:27 +0000

Max wrote: “I am skeptical that there is enough air to provide lift,”

The test shown in the second half of the video embedded in the article was performed in a vacuum chamber in order to verify that the drone could fly in a thin atmosphere. This was not very clear in the video. I am a little concerned that it may tip over on landing. Can it right itself?

Although I agree that a balloon would last a long time (hydrogen would leak out more slowly than helium), it seems that our scientists are not yet ready for the arbitrary nature of what could be studied via a balloon adrift on the wind.

By: Max

Max — Sat, 12 May 2018 05:09:26 +0000

We were just talking about this recently.
I am skeptical that there is enough air to provide lift, the low gravity of mars will help. nearly 4 pounds is a challenge but the design looks right. I expected thicker blades but the high rpm’s should compensate. If it tips over…

Details from the article;
“Started in August 2013 as a technology development project at NASA’s Jet Propulsion Laboratory, the Mars Helicopter had to prove that big things could come in small packages. The result of the team’s four years of design, testing and redesign weighs in at little under four pounds (1.8 kilograms). Its fuselage is about the size of a softball, and its twin, counter-rotating blades will bite into the thin Martian atmosphere at almost 3,000 rpm — about 10 times the rate of a helicopter on Earth.”

Very exciting, just what they need to examine the entrance to lava caves and sinkholes.
If this works out, I’m sure a design can be created were a light solar panel/battery could be carried independently as a charging station to distant locations of interest, where the charging station could separate to collect energy by day while the much lighter drone scouts the formations, hopping from interest to interest, and returns.

I still think a Mylar balloon with helium lift and communication system similar to the cell phone in the watch, powered by a solar panel on top of the balloon.
If the balloon loses lift during the cold of the night, there might be an option of a microgram of plutonium placed inside the battery which would not only create power, but heat to keep the balloon aloft.
Such a thing would drift with the wind patterns but may have the ability to stay alive for years, covering a great distance.