Author Topic: ARCA  (Read 132944 times)

Offline Steven Pietrobon

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Re: ARCA
« Reply #40 on: 09/02/2020 08:15 am »
I'm not following this super close... but is there plan to do a "hot fire" (steamy fire?) with the vehicle secured to the ground with ropes? Then more ropes on the side to stabilize it? All of which is in or very close to the exhaust path?

The purpose of the test is to test the attitude control system of the engine (pitch, roll and yaw). The engine will be flying "free" in the test stand. In case something goes wrong, the engine will be limited in how high it can fly with tie down ropes attached to the base of the engine, to prevent the engine from crashing into the top of the stand. Ropes attached to the side of the engine will limit lateral movement.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Steven Pietrobon

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Re: ARCA
« Reply #41 on: 09/20/2020 12:31 pm »
ARCA have performed their first test in the stand. Unfortunately, the tank leaked at 185 kPa so they decided to do a short engine test with the engine tied down. You can see the leak at bottom left of tank. The first photo is of their team psychologist. The last photo is in their control hub.

Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Online ringsider

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Re: ARCA
« Reply #42 on: 09/20/2020 02:57 pm »
Can anyone explain what exactly it we are seeing in that video?

Is it basically a hot shower?

Offline matthewkantar

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Re: ARCA
« Reply #43 on: 09/20/2020 04:23 pm »
Can anyone explain what exactly it we are seeing in that video?

Is it basically a hot shower?

Aquaspiketm technology?

Offline Lars-J

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ARCA
« Reply #44 on: 09/20/2020 07:57 pm »
Can anyone explain what exactly it we are seeing in that video?

Is it basically a hot shower?
Yes.

Watched the video... The charade continues. A “hop”? Please. There appeared to be little thrust at all, it did not move much. (If anything it moved down after the “ignition”)

And then the guy is talking about comparing it with “simulations in his mind”. So this thing is controlled with a joystick? Have there been no software simulations?

No, this thing will never do a free flight, even if the thrust would be sufficient.
« Last Edit: 09/20/2020 08:07 pm by Lars-J »

Offline Pueo

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Re: ARCA
« Reply #45 on: 09/20/2020 08:29 pm »
An aerospike for an engine that will only operate from the ground to an altitude of 3 km?  Did I get that right?

That doesn't make any sense.

This is effectively a pressure rocket right?  While the atmospheric pressure doesn't change the "chamber pressure" probably drops significantly over the course of the firing leaving the plume over-expanded.  It could be that an aerospike is the correct choice over a bell nozzle given the rest of the design restrictions.

Also their tank that needs to hold 4000 kPa failing at 185 kPa is a pretty big issue to work out.
« Last Edit: 09/20/2020 08:40 pm by Pueo »
Could I interest you in some clean burning sub-cooled propalox and propalox accessories?
Forget drinking ethanol meant for rocket fuel, propÆne is the eutectic fuel mixture you can huff!

Offline Fizrock

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Re: ARCA
« Reply #46 on: 09/20/2020 08:44 pm »
An aerospike for an engine that will only operate from the ground to an altitude of 3 km?  Did I get that right?

That doesn't make any sense.

This is effectively a pressure rocket right?  While the atmospheric pressure doesn't change the "chamber pressure" probably drops significantly over the course of the firing leaving the plume over-expanded.  It could be that an aerospike is the correct choice over a bell nozzle given the rest of the design restrictions.

Also their tank that needs to hold 4000 kPa failing at 185 kPa is a pretty big issue to work out.
 
 
It's significantly worse then a pressure rocket. This thing has an ISP 20s (yes, you read that correctly). They'd get way more performance if they just made a huge pressure bottle and let the air out.
 
It also has a TWR of ~2, and I don't think their mass figure even includes all the batteries they'd need. So far they've been using ground power.
« Last Edit: 09/20/2020 08:50 pm by Fizrock »

Offline launchwatcher

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Re: ARCA
« Reply #47 on: 09/20/2020 08:47 pm »
Can anyone explain what exactly it we are seeing in that video?

Is it basically a hot shower?
Yep.

I'm increasingly convinced this thread is in the wrong section of the forum.   New Physics is perhaps the best match.

Offline xyv

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Re: ARCA
« Reply #48 on: 09/20/2020 09:36 pm »
Or the humor section that this site doesn't have.  Seriously, these guys are entertaining.  Tank leaks at less than a car tires' pressure...team psychologist,,,"we had a leak at 1.85 bar but decided to fire the engine anyway..."?  Who does that with an actual rocket engine?

This whole thing feels more like a Borat style You-tube prank but I am loving every bit of it.

Offline TrevorMonty

Re: ARCA
« Reply #49 on: 09/20/2020 10:29 pm »
Or the humor section that this site doesn't have.  Seriously, these guys are entertaining.  Tank leaks at less than a car tires' pressure...team psychologist,,,"we had a leak at 1.85 bar but decided to fire the engine anyway..."?  Who does that with an actual rocket engine?

This whole thing feels more like a Borat style You-tube prank but I am loving every bit of it.
Being steam powered its not a fire risk if anything goes wrong.

Offline ChrisWilson68

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Re: ARCA
« Reply #50 on: 09/20/2020 10:58 pm »
Or the humor section that this site doesn't have.  Seriously, these guys are entertaining.  Tank leaks at less than a car tires' pressure...team psychologist,,,"we had a leak at 1.85 bar but decided to fire the engine anyway..."?  Who does that with an actual rocket engine?

This whole thing feels more like a Borat style You-tube prank but I am loving every bit of it.
Being steam powered its not a fire risk if anything goes wrong.

That's because it uses pressure instead of chemical to store its energy.  Hot steam and the kinetic energy of a failed pressure vessel are every bit as capable of causing damage and injury as a fire.

The only reason this thing could be considered any less dangerous than a typical chemical rocket is that it has way less energy than a typical chemical rocket because it has way less performance.  For a chemical rocket of the same energy, it's no less dangerous.

Offline CameronD

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Re: ARCA
« Reply #51 on: 09/20/2020 11:22 pm »
So, apart from the pretty logo on the front indicating it's part of their uniform, what's with the helmets?!?

"The sky is falling!!"  ;D
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline ChrisWilson68

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Re: ARCA
« Reply #52 on: 09/20/2020 11:27 pm »
So, apart from the pretty logo on the front indicating it's part of their uniform, what's with the helmets?!?

"The sky is falling!!"  ;D

It's showmanship.  It's meant to invoke the idea that they're in a simulation of what it would be like if they were in a capsule on top of the water tank, steering their steam rocket with a joystick.

They're clearly trying to appeal to people with limited knowledge of spaceflight.

Offline Steven Pietrobon

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Re: ARCA
« Reply #53 on: 09/21/2020 07:48 am »
Watched the video... The charade continues. A “hop”? Please. There appeared to be little thrust at all, it did not move much. (If anything it moved down after the “ignition”)

There was some vertical movement, as the electrical connectors at the base disconnected as planned. Due to the low pressure, a significant height increase was not expected to be achieved. The actual tests are planned to be as follows:

Test 1. Full manual control, operated by Airbus A320 pilot. Increases thrust from 0 to 10% and holds for 3 seconds. Slowly reduces throttle to maintain level flight for 4 to 5 seconds. Slowly reduces thrust to 0.

Test 2. Manual roll, pitch and yaw test.

Test 3. Automatic roll, pitch and yaw test.

Test 4. Takeoff from pad and land on landing gear.

Cords are attached to base of engine to prevent engine from hitting stand during tests.

Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Steven Pietrobon

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Re: ARCA
« Reply #54 on: 09/21/2020 08:08 am »
It's significantly worse then a pressure rocket. This thing has an ISP 20s (yes, you read that correctly). They'd get way more performance if they just made a huge pressure bottle and let the air out.
 
It also has a TWR of ~2, and I don't think their mass figure even includes all the batteries they'd need. So far they've been using ground power.

According to their white paper, the LAS 25D testbed has an Isp of 50 s and a thrust to weight ratio (TWR) of 13.9 (including tankage, but not propellant). The LAS 25R to be used as the first stage of their small launch vehicle has an Isp of 67 s and a TWR (including batteries and tankage) of 10.4. TWR including propellant for LAS 25D is 2.55, which is more than enough to take off.

LAS 25R is expected to take the second stage to 3 km altitude at 390 m/s. Compare this to Virgin Orbit which takes their vehicle to 10.7 km and 270 m/s. In terms of energy (m*g*h+m*v²/2), LAS 25R is only 25% less than that provided by a Boeing 747 for the same mass.
« Last Edit: 09/21/2020 08:26 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Re: ARCA
« Reply #55 on: 09/21/2020 03:46 pm »
Why would you put an aerospike on a rocket that only travels up 3km?

Listen, the idea of using a large steam rocket as a cheaper (and probably reusable) alternative to SRBs is interesting to me too. But this thing isn't that. It is at best, a poor replacement for air-launch. And at worst it's an outright scam.
Wait, ∆V? This site will accept the ∆ symbol? How many times have I written out the word "delta" for no reason?

Offline edzieba

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Re: ARCA
« Reply #56 on: 09/21/2020 04:35 pm »
Arca have a core intriguing concept (low-cost first stage using phase transition of supercritical water to steam), surrounded by a whole load of periphery utter nonsense (aerospike nozzle, the ludicrous control centre, supernumery staff roles, almsoty all of the output from their PR, etc).

Offline ChrisWilson68

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Re: ARCA
« Reply #57 on: 09/21/2020 04:40 pm »
Arca have a core intriguing concept (low-cost first stage using phase transition of supercritical water to steam), surrounded by a whole load of periphery utter nonsense (aerospike nozzle, the ludicrous control centre, supernumery staff roles, almsoty all of the output from their PR, etc).

I agree it's worth discussing.  But to me, something that lowers cost isn't very intriguing if it lowers performance even more.  I think their steam rocket stage falls into that category.

Offline rklaehn

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Re: ARCA
« Reply #58 on: 09/21/2020 04:55 pm »
If the actually build this, even in with the limited performance, it should be quite a big show.

So as long as they don't spend taxpayer money, I fail to see the problem.

It is a bit preposterous to call a rocket that does not even make it into the stratosphere a "launch vehicle" though...

Offline ChrisWilson68

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Re: ARCA
« Reply #59 on: 09/21/2020 05:10 pm »
If the actually build this, even in with the limited performance, it should be quite a big show.

So as long as they don't spend taxpayer money, I fail to see the problem.

It is a bit preposterous to call a rocket that does not even make it into the stratosphere a "launch vehicle" though...

I don't think anyone is calling for them not to be allowed to waste their money if they want to.  They have the right to waste their own money.

But people who think it's a waste also have a right to make that point.  Arca tries to get contributions from the general public, and it's a public service to get out the message that they're wasting money.

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