Ask HN: Making a low cost interplanetary "weather balloon"? | Hacker News Reader

Ask HN: Making a low cost interplanetary "weather balloon"?

4 pointsmanaskarekar5 comments

A childish indulgence, but something I have thought about over and over again and wondered, it's hard, sure, but really, how hard?

Putting stuff in orbit and maintaining it there obviously needs a lot of precision, resources, hard work. But what about 'weather-balloon' like bare minimum project whose goals could be something like:

1. Have goals that do not require a ton of precision, for example go as far as possible, take as high resolution pictures as possible etc.

2. Not worry about losing the craft, perhaps eventually just crashing into the planet and sending that information back. 'Do one thing and do it well' goals of all sorts.

3. Be cheap enough that multiple of them could be sent to account for failure, so more of a spray-and-pray approach as opposed to making one single craft that is absolutely bullet proof.

Required stuff that comes to mind:

1. A rocket with tons of fuel to leave earth.

2. A very very tough ball/craft to reduce drag while dropping onto various "space rocks" and weather small impacts.

3. Shielding from known interference/damage causing factors.

4. A propulsion system for the craft in space - Solar/Nuclear/Magic?

5. Tons of redundant sensors/cameras depending on what the minimal set of goals for the project are.

6. A rock solid high power communication/relay mechanism.

7. A bare minimum navigation system. Perhaps a self destruct mechanism to not fuck up other big missions (NASA/SpaceX) etc?

Sounds pretty damned childish and perhaps like every kid's fantasy, I know, but would love to hear any thoughts on how outlandish it really is.

What you've outlined is the "Faster, Better, Cheaper" policy. You can read some about that history at http://amyshirateitel.com/2012/03/06/should-nasa-reconsider-... .

The basic problem is that it costs something like $2,000/kg to get something out of earth orbit, and 1 kg doesn't get you much. For example, a literal "ton" of redundant sensors would cost $2 million. Just the launch cost for Galileo (to Jupiter) would have cost $50-$100 million or so of its $1 billion cost.

Instead of having "tons of fuel", the cheaper option is to use complex orbits that take advantage of gravity boosts. This allows more weight for sensors and less for boring fuel. But it can take more time.

There's little need to self-destruct. It's expensive to carry a bomb out to Jupiter. Instead, we 'deorbited' Galileo into the planet when its mission was over.

The spacecraft isn't the only cost. There's also time on the Deep Space Network to be able to send and receive messages with the craft, and people to maintain things and analyze the data.

You could make it cheaper on the ground by using a higher power communication system. However, that makes the craft heavier, which costs more money, and reduces what else the craft can do. Rather than having enough power to transmit flyby data live, it's better to use a lower power system and send the data over several weeks. After all, in most of space there's a whole lot of nothing going on.

There is no drag in space. Shape doesn't make a difference.

You can see now some of why mission planning can be very complicated. More fuel means fewer sensors and less transmission capability, but can make a shorter trip or give more maneuverability at the end. These can all affect the mission goals.

Most of it I can see working - going faster/further does basically come down to adding more fuel or reducing payload.

The navigation and communication would be where you run into problems. I note that you have specified that as rock solid, unlike the other aspects. Over long distances, communication needs to be directional - you have to know exactly where the spacecraft is (perfect navigation) or it sends no data back and therefore isn't doing anything useful.

Interestingly, this issue doesn't apply to a manned spacecraft that can make unexpected changes without being in contact with Earth, but that doesn't fit too well with the redundant/disposable concept.

   A silly thought:

 We currently don´t have the tech to build a practical

space elevator, but what about one for small payloads, for these bare minimum projects?

There's no such thing as a small scale space elevator. The difficulty in reaching orbit or elsewhere in the solar system is not altitude, but enough horizontal velocity to continually fall and miss the earth or reach escape velocity entirely.

A space elevator must stretch to at least geosynchronous altitude which is 35,800 km. Low earth orbit of 300 km sounds like 1% the effort, but does not help. The top of a 300 km structure on the equator would move at only 0.25 km/sec, nowhere near the 4 km/sec needed for orbit. (It could help if you built a launcher or railgun on top of it, outside the atmosphere, to skip air friction, but it can't literally elevate you into orbit.)

  I didn't mean small scale as in not reaching orbit with it, but as having a small payload.
  I thought the weight of the elevator and its maximum payload with available materials were what keeps it from being built today.

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