ARCA Space Corporation

[matthewkantar]

That is hilarious. Rutan wants his windows back.

[BrightLight]

Remember that it's critical to have a stealth aircraft take off from water to launch a rocket (water proof!) to orbit, Thunderbirds are go

[ringsider]

Remember that it's critical to have a stealth aircraft take off from water to launch a rocket (water proof!) to orbit, Thunderbirds are go

I will just drop this here:-

http://www.parabolicarc.com/2016/09/19/norwegian-company-working-ocean-launched-rocket/

[Welsh Dragon]

Launching from water isn't in itself a problem for a well designed rocket, see Seabee and Seahorse. It's the combination of a stealth seaplane with under-slung rocket that's rather... out there.

[ANTIcarrot]

Reported by Newatlas suspiciously close to April first, but...

ARCA space corporation has a blueprint for an expendable SSTO with a lift off mass of 16.3 tons capable of putting ~50kg into orbit. (For an given definition of orbit presumably.) The design weight would be 510kg empty, and would run on HTP/RP-1 using a linear aerospike. Another version of the rocket would fly with 2 stages and a heavier payload.

Size, weight, cargo, and fuel look oddly similar to the UK Black Arrow, save that was a three stage launcher, and had an empty weight closer to 1.7 tons. Given the Black Arrow was built on a shoe string, in the late 60s, and was possibly over-engineered, there might be some mass savings to be made there, but 1.2 tons?

Carbon fibre woudl produce some weight reduction, as well as building it so it properly crumples on impact rather than just getting slightly dented. Balloon tanks supposedly produce some weight saving, but can't find any actual numbers.

Latter might be worth talking about even if the rest is pie in the sky. Has anyone got any hard numbers for exactly how much savings balloon tanks provide? And has anyone actually tried building a carbon fibre balloon tank? Cryo or otherwise.

[Asteroza]

Is there even an advantage to a linear aerospike over a toroidal aerospike for a simple cylinder body?

[matthewkantar]

This showed up on Youtube after I watched the video linked above.



This all worked out well didn't it?

Matthew

[kch]

Is there even an advantage to a linear aerospike over a toroidal aerospike for a simple cylinder body?

Roll control. 

[savuporo]

Is there even an advantage to a linear aerospike over a toroidal aerospike for a simple cylinder body?

Roll control. 

No, the CGI looks better.

[sevenperforce]

Cool! They are using liquid Helium, heated in the engine to make gaseous Helium to pressurise the tanks. This is what SpaceX should be doing. For SSTO though, my research indicates using LOX/RP-1 gives better performance than HTP/RP-1.

SpaceX did use liquid helium heated in an engine heat exchanger to pressurize the tanks for the pressure-fed Kestrel engine. And SpaceX still uses a heat exchanger to increase the helium pressurant efficiency in the Falcon 9 first and second stages, though the heat exchanger is in the Merlin's gas generator rather than in the chamber.

Pressure-fed designs don't typically make sense for large stages, but with a composite tank/body and an aerospike engine, it's not a bad idea. The aerospike engine's high expansion efficiency means a lower chamber pressure (required for pressure-fed designs) is less punishing, and a pressure-fed design saves the mass of a turbopump, which makes up for the aerospike's lower TWR.

True, HTP/RP-1 has lower specific impulse than kerolox, but it's one of the only non-exotic combinations that has higher thrust than kerolox, which is important for the heavy aerospike engine. HTP is also cheaper than LOX, and while it has its own handling challenges, it's less challenging from a materials standpoint than LOX.

So...yeah. If you're going to do an expendable SSTO on the cheap, this isn't a half-bad way to go about it. I could try to throw together some speculative maths on this to get an idea of what sort of mass fraction it would need to hit, based on known engineering.

Whether this company has the capability for anything like this...well, that's another matter entirely.

I could see an SSTO of this type being used in combination with a SEP LEO bus to grapple comsats and toss them into a useful orbit.

Is there even an advantage to a linear aerospike over a toroidal aerospike for a simple cylinder body?

Roll control. 

A single-chamber toroidal aerospike has no control authority at all; a multichamber toroidal aerospike has pitch and yaw authority but no roll authority. A multichamber linear aerospike has pitch, yaw, and roll authority with no moving parts, simply by differential throttling. And for a pressure-fed design, that works rather well.

EDIT: For all their whining about the horrors of staging, this particular design could benefit greatly from the optional addition of some strap-on COTS parallel SRBs. For small LEO comsats you could just use the base configuration; for larger payloads you simply charge the customer for adding 2 or 4 SRBs as needed. Much simpler and cheaper than worrying about adding a second stage.

[sevenperforce]

Looking for red flags in these specs:

Length: 16 m
Diameter: 1.5 m
Dry mass: 550 kg
Launch mass: 16,290 kg
Payload mass: 100 kg
Engine: Pressure-fed linear aerospike
Nozzle: 80:1 expansion ratio, 80% cut
Engine coolant & pressurant: Liquid helium
Number of chambers: 16
Nozzle cooling: Ablative + RP-1 film
Propellant: HTP + RP-1
Burn duration: 272 s
Thrust (SL): 22,920 kgf
Thrust (vac): 33,500 kgf
Isp (SL): 230 s
Isp (vac): 314 s
Propellant flow rate: 100 kg/s
Mixture ratio: 7.46:1
Tank pressure: 20 barg
Chamber pressure: 16 barg

[ChrisWilson68]

Looking for red flags in these specs:

Length: 16 m
Diameter: 1.5 m
Dry mass: 550 kg
Launch mass: 16,290 kg

That dry mass seems awfully optimistic to me.

[sevenperforce]

Looking for red flags in these specs:

Length: 16 m
Diameter: 1.5 m
Dry mass: 550 kg
Launch mass: 16,290 kg

That dry mass seems awfully optimistic to me.

Yeah, it does seem optimistic to me as well. That's only 12% more dry mass than the ITS Tanker, which has higher TWR engines, a lower vehicle TWR, and a huge square-cube advantage. Then again, the ITS Tanker also has TPS and RCS systems, which the ARCA rocket wouldn't have to bother with. HTP is also a great deal denser than LOX, so that helps a bit.

Anyone have an idea of ballpack TWR for a pressure-fed linear aerospike?

If ARCA added disposable air augmentation shrouds -- panels, really -- jettisoned at the same time as the payload fairing, they could make up for that horrible SL specific impulse. I bet that mixture ratio optimization could help as well.

[GWH]

Interesting in that rocket lab chose battery powered pumps over pressure fed due to overall mass savings and even with composite structures.
Given that they are using HTP I wouls have thought decomposition driven turbopumps would be the most efficient solution.

[sevenperforce]

Interesting in that rocket lab chose battery powered pumps over pressure fed due to overall mass savings and even with composite structures.
Given that they are using HTP I wouls have thought decomposition driven turbopumps would be the most efficient solution.

Does RL's Electron use composite tanks or aluminum tanks? Composites, as with the ARCA vehicle, work much better with pressure-fed designs than aluminum, so that's one reason.

I'm guessing the increased dry mass of the turbopump alone would be greater than the added mass of the full liquid helium tank. The composite tank can probably handle the pressure without needing to be any thicker than it would otherwise be. HTP has poor enough specific impulse as it is; reducing its efficiency by decomposition would make it even worse.

[GWH]

Interesting in that rocket lab chose battery powered pumps over pressure fed due to overall mass savings and even with composite structures.
Given that they are using HTP I wouls have thought decomposition driven turbopumps would be the most efficient solution.

Does RL's Electron use composite tanks or aluminum tanks? Composites, as with the ARCA vehicle, work much better with pressure-fed designs than aluminum, so that's one reason.

I'm guessing the increased dry mass of the turbopump alone would be greater than the added mass of the full liquid helium tank. The composite tank can probably handle the pressure without needing to be any thicker than it would otherwise be. HTP has poor enough specific impulse as it is; reducing its efficiency by decomposition would make it even worse.

Electron is composite construction.  Somewhere in discussion on the vehicle some one calculated mass of the vehicle with required wall thickness for pressure fed vs without and found that even with the added mass of batteries it was a much more mass efficient option.

[sevenperforce]

Hmm. They are about the same size. The ARCA vehicle is a bit smaller but significantly heavier -- due to the HTP replacing the less dense LOX -- so it has more to lose in the engine dry mass department than Electron.

[ChrisWilson68]

Well, Electron also isn't SSTO, so it has far more margin to play with.

[savuporo]

Well, Electron also isn't SSTO, so it has far more margin to play with.

It also exists, which constrains it to laws of physics

[Steven Pietrobon]

HTP is also cheaper than LOX, and while it has its own handling challenges, it's less challenging from a materials standpoint than LOX.

I'm pretty sure rocket grade HTP is more expensive than LOX. 85% HTP costs $8.27/kg in a 30 kg lot, although should come down for higher volumes. Google says that LOX is $0.16/kg.

http://www.peroxidepropulsion.com/hydrogen-peroxide.php

With a propellant mass of 15,640 kg and a mixture ratio of 8.2 to 1 (the same as the British Gamma engine), that gives a HTP mass of 13,940 kg and a upper bound of the cost of $115,284.