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Dynetics vehicles and discussion

tater

By tater
in Science & Spaceflight

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DBowman

DBowman

Posted
Posted (edited)

They are advertising for propellant fluid engineers and main engine pump engineers with cryo & hydrocarbon fluids experience. I'm guessing methane oxygen.

Edited by DBowman
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sevenperforce

sevenperforce

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  On 5/2/2020 at 6:48 AM, kerbiloid said:

So many engines...
Probably they use Throttle Controlled Avionics mod.

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Hah!

In all seriousness I wonder if these engines are intended to be throttleable or not. An easy way to get throttleability is to use multiple engines and shut down some of them, so they will probably be cheaper and lighter if they aren't throttleable. But if not then they'll need gimbal. If they are throttleable then they'll be able to use RCS for roll and throttle for pitch and yaw. 

  On 5/2/2020 at 7:25 AM, DBowman said:

They are advertising for propellant fluid engineers and main engine pump engineers with cryo & hydrocarbon fluids experience. I'm guessing methane oxygen.

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Nice catch.

A single pump for each quartet of engines is lighter but multiple redundant pumps is more reliable.

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RCgothic

RCgothic

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  On 5/2/2020 at 1:56 PM, sevenperforce said:

An easy way to get throttleability is to use multiple engines and shut down some of them, so they will probably be cheaper and lighter if they aren't throttleable. But if not then they'll need gimbal. 

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Not necessarily. Shut them down in pairs opposite sides of the COM. With 8 engines you then have 4 throttle settings plus off.

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sevenperforce

sevenperforce

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  On 5/2/2020 at 3:27 PM, RCgothic said:

Not necessarily. Shut them down in pairs opposite sides of the COM. With 8 engines you then have 4 throttle settings plus off.

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That was my point. You can "throttle" by pairwise startup and shutdown, which means you don't (really) need throttleability for the landing burn. Non-throttleable engines are cheaper, lighter, more efficient, and less fault-prone. However, individual shutdowns and startups don't provide fine enough control to provide immediate pitch and yaw authority. So if they are non-throttleable, then they need gimbal, or the lander needs to rely exclusively on RCS for pointing.

If they used fixed but throttleable engines then they have to use RCS for roll but can use differential throttling for pitch and yaw. They can get roll control if they cant out some of the engines slightly, but that introduces cosine losses.

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sevenperforce

sevenperforce

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  On 5/3/2020 at 4:49 AM, kerbiloid said:
  On 5/2/2020 at 11:18 PM, RCgothic said:
  On 5/2/2020 at 7:18 PM, kerbiloid said:

They could make all eight gimbal and change the net thrust by tilting them radially all at once.

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You'd need a heck of a lot of gimball - 35° off-axis just to get to 80% thrust.

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But you need this only on landing,

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Oh, so not like the new Poodle at all.

 

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sevenperforce

sevenperforce

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  On 5/5/2020 at 7:25 PM, tater said:

Looks like 4 per side. Top down view (O = firing):

      FRONT

X  O          X  X

X  O          O  O

 

Differential thrust for control?

 

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Looks like it to me.

They don't appear to gimbal. Though at this point they don't really have the engines themselves so all that is spec.

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tater

tater

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  On 5/5/2020 at 7:31 PM, sevenperforce said:

They don't appear to gimbal. Though at this point they don't really have the engines themselves so all that is spec.

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LOL.

Still, of the 2 (3 if you count whatever Boeing was working on) "old school" landers, I like this one best.

Starship is a dark horse here, but the payoff should it work is nothing short of epic.

This lander could fly a cargo version sort of like a skycrane helicopter. Leave a hab pod, return to Gateway. Leave a dense packed cargo pod, return to Gateway. Since the ascent stage would be just the framework, more cargo to the surface would be possible.

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sevenperforce

sevenperforce

Posted
Posted
  On 5/5/2020 at 7:41 PM, tater said:

This lander could fly a cargo version sort of like a skycrane helicopter. Leave a hab pod, return to Gateway. Leave a dense packed cargo pod, return to Gateway. Since the ascent stage would be just the framework, more cargo to the surface would be possible.

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Agreed. 'Twas my proposal a few months ago. Use the same architecture to support cargo drops as you use for your human ascent element; common architecture helps demonstrate function and work out kinks. Drop-tank-based architecture beats propellant transfer unless you are literally Starship.

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