The thread for space cadets!

[stfoskey12]

You can't actually, unless you have on board propulsion and even then it's a losing proposition. When you spin up the wheel, it will cause the bus to spin by applying a torque to the bus. You can stop this bus spin with propulsion. To extract the energy back out of the flywheel, you could slow down the wheels with electromagnetic braking but again this would impart a spinning torque to the bus that you would have to use propulsion to offset.

In between spin up/spin down, the wheel would tend to hold the bus in a stable pointing attitude but this scheme doesn't work because the cost of bringing the extra fuel mass more than offsets the power gain (really not a gain, trading rotational kinetic energy for released chemical energy) and adds mass. Also, for the wheels to be big enough to hold the bus stable purely on their own momentum, they have to be very heavy, further adding cost and mass - and the larger your mass, the more propulsion you need an so on.

A reaction wheel is a type of flywheel where you spin a mass to impart a torque on the bus, allowing it to change pointing attitude without expending propellant. But they can only spin so fast before they fail, which means there are limits to how much pointing you can do.

What's a bus in this case?

 

[Imaus]

RTGs? For trans-Neptunian high-rez telescopes? Just throw them up with lightweight nuclear reactors; go the whole field. Ditto with relay sats mid-way to help keep data rates high.

 

[hobbsyoyo]

So correct me if I am wrong.
The brake could be electromagnetic which could generate a small amount of electricity; I assume that such a system could be used to spin it up in the first place but would be more complicated.
What happens to the power that you input into the flywheel if you do not recover it when you slow it down. I assume you do not want to warm things up then let them cool down again as this will add to ware and tear so it is better to control heat production.

Regenerative braking is not common on satellites and implementing it would turn into a major development program for anyone that went down that path. It's a simple enough concept but it is not actually that easy to implement. And you won't get as much power out of the wheels as you think - a few watts to tens of watts for a few seconds to minutes. This isn't worth the cost to implement in complexity, development time or R&D capital. It will make the bus less reliable and adversely affect the propulsion requirement by inflating propellant needs.

And yes, typically satellites just absorb the waste heat from braking reaction wheels. It's not usually a limiting case for the bus.

This satellite is going to be working for fifty years with maybe no further contact.
The extra weight of a flywheel system that can recover some of its energy is a fixed weight cost no matter how long the mission lasts.

I don't really know what you mean by fixed weight cost here. Adding this system will make the satellite less durable - simpler is almost always better.

Assuming no external power source (sun) the propellant weight cost will be an increasing cost dependent on the planned length of the mission.

Are you talking about using solar sails for propulsion? Past Neptune?

Electric propulsion can be used to reduce the amount of propellant required.
At some point the extra weight of a more complicated flywheel system will have offset the amount of propellant required.

Electric propulsion requires huge batteries, huge RTGs or both. It's maybe viable if all you are doing is dumping reaction wheel momentum but it's an iffy trade.

 

[hobbsyoyo]

What's a bus in this case?

Sorry I threw out random jargon and please continue calling me out on it.

A 'bus' can mean a few things, including:

1. The body of a satellite, minus extraneous things like solar arrays and antennas
2. The entire satellite
3. A section of avionics, either computer interfaces or a voltage rail (power source)

In this instance I meant number 2.

RTGs? For trans-Neptunian high-rez telescopes? Just throw them up with lightweight nuclear reactors; go the whole field. Ditto with relay sats mid-way to help keep data rates high.

Relays make a lot of sense. I think a nuclear reactor would make sense as well but it's not a sure thing. It would come down to how low you could get your power consumption requirements for the satellite. Lower power favors RTGs as they're smaller and simpler but don't produce a lot of juice.

 

[Goodfella]

Falcon Heavy money shots:

 

[Broken_Erika]

Stratolaunch: 'World's largest plane' lifts off for the first time

The world's largest aeroplane by wingspan has taken flight for the first time.

Built by Stratolaunch, the company set up by the late Microsoft co-founder Paul Allen in 2011, the aircraft is designed to act as a flying launch pad for satellites.

The idea is to fly the plane to 10 km (6.2 miles) high before releasing satellites into orbit.

Its 385 ft (117 m) wingspan is the length of an American football field.

• Microsoft founder announces space venture
• The billionaires fuelling a space race

If successful, such a project would be a cheaper way to launch objects into space than rockets fired from the ground.

The twin-fuselage six-engine jet flew up to 15,000 ft (4,572m) and reached speeds of about 170 miles per hour (274 km/h) on its maiden flight.

https://www.bbc.com/news/world-us-canada-47923697

 

[hobbsyoyo]

Yup but it doesn't have a rocket to go with it. Northrup is allegedly going to launch Pegasus XL rockets from it but they already have their own carrier plane for that so I can't see it being a long-term project. Plus the Pegasus XL is extremely expensive (the cost of an F9 with like 1/50th the lifting capacity) and unreliable. They were supposed to launch one back in Nov or Dec or something and it's still in the hangar as it had issues when they went to launch it.

They were designing their own rockets to make use of the plane's enormous lifting capacity but they cancelled them as soon as Paul G Allen died - which to me is pretty disrespectful of him. Maybe he didn't leave the company enough money to continue with their plans but given his commitment to Stratolaunch and his ongoing health issues before he died, I find it hard to believe.

 

[red_elk]

Video from Egyptsat on-board camera

Ion thrusters working, at 0:54

 

[hobbsyoyo]

Very cool video!

 

[Cutlass]

 

[hobbsyoyo]

The center core of the Falcon Heavy rocket landed successfully but tipped over in rough seas. The top 2/3 of it sheared off and Elon has speculated they might attempt to salvage the engines which are the most expensive part of the rocket.\

Another Chinese start-up mounted a launch attempt and failed. The government is doing their start-up rocket scene a huge favor by offloading ICBM stages on them for testing purposes.

 

[Goodfella]

Sounds like some major delays are in store for Demo 2.

https://www.google.com/amp/s/arstec...s-had-an-anomaly-during-tests-saturday/?amp=1

 

[Michkov]

The center core of the Falcon Heavy rocket landed successfully but tipped over in rough seas. The top 2/3 of it sheared off and Elon has speculated they might attempt to salvage the engines which are the most expensive part of the rocket.\

I take it the the stages are not fixed to the barge once they are recovered?

 

[Cutlass]

I take it the the stages are not fixed to the barge once they are recovered?

They'd have to cool down before they can be secured.

 

[hobbsyoyo]

Sounds like some major delays are in store for Demo 2.

https://www.google.com/amp/s/arstechnica.com/science/2019/04/spacexs-crew-dragon-spacecraft-has-had-an-anomaly-during-tests-saturday/?amp=1

There is a video floating around on twitter that I can't seem to find at the moment -

It looks like they were going to do a static fire of the capsule that was sent to the ISS a couple months back and it exploded. From the video, it appeared the whole thing tore apart. Boeing's surrogates within Congress are going to absolutely murder SpaceX over this and there's now a chance Boeing will get astronauts to the station first. Unless they can show this was an operational error, the investigation and resulting action items are going to take ~6 months to resolve, and the overall delay to their schedule might be close to a year. That's my ball park guess though.

Coincidentally, Boeing had their own pad explosion of their capsule but no footage of it exists and people aren't as hyped about the Starliner as they are Crew Dragon so it flew under the radar. It did cause them significant delays but it was not reported on or talked about to anywhere close to the extent that this Crew Dragon explosion already is.

I take it the the stages are not fixed to the barge once they are recovered?

They'd have to cool down before they can be secured.

Usually, they have a robot called the octograbber come out of a little shed on the deck of the barge and it goes out and grabs the booster and secures it. The octograbber is not compatible with Falcon Heavy's center core, however, so it was unsecured. Without the octograbber, they have to send people onto the deck to weld the booster feet to the ship but due to the rough seas, the booster was squirming around and it was unsafe to put people on the deck. I don't think engine cool-down requires very long, I think venting gases and ensuring all valves in their correct state is the main schedule driver. Either way, none of that was the issue here, the hold up was the really rough seas.

Octograbber:

Spoiler octograbber :

In other explosive news - that Boeing satellite up in geostationary orbit called Intelsat 29e that was reported to have issues has now been declared a total loss. After the disruption to service, the satellite was shown to have exploded through telescopic observation and there are now several large pieces of it floating about the geostationary arc along with the dead satellite itself.

 

[hobbsyoyo]

Sorry, what I meant is that the video of the Boeing test anomaly has not been leaked to the press in the way that the SpaceX failure has. I'm sure video of the Boeing anomaly exists, just not publicly.

Here's a link to leaked video of the SpaceX explosion (twitter won't let me embed it):
https://twitter.com/Astronut099/status/1119825093742530560

This video is the best Easter gift Boeing could have asked for.

 

[hobbsyoyo]

I hope this wasn't a COPV* problem. A COPV is what took down the Amos-6 rocket (the on-pad explosion) and NASA has expressed a ton of concern about Falcon's COPVs during their certification for manned flight. If a COPV burst inside Dragon then it will undo a lot of that certification work or at least jeopardize it. I am not sure the Dragon uses COPV's though, it might use (safer, but heavier) all-metal tanks for gas storage.

*carbon overwrapped pressure vessel - bottles used to store high-pressure gases like helium and nitrogen

 

[Goodfella]

I’m pretty sure they do have COPVs on Dragon.

 

[hobbsyoyo]

China built a Mars simulator in the Gobi desert. They are using it for educational purposes right now and plan to expand it to cover a 67 km2 area.
https://qz.com/1597863/inside-chinas-mars-simulator-camp-in-the-gobi-desert/
There are many more cool pictures if you follow the link. Here are a few choice ones:

Spoiler :

Spoiler :

Spoiler :

Spoiler :

 

[Broken_Erika]

I like the Stormtrooper armor.