Stoke Space

[tater]

They plan on hop tests for their stage 2.

[Rutabaga22]

3 hours ago, tater said:

They plan on hop tests for their stage 2.

Are they landing stage 2?

[Beccab]

8 minutes ago, Rutabaga22 said:

Are they landing stage 2?

Yup, that's the reason it has an aerospike-ish (more like plug nozzle)

[JoeSchmuckatelli]

5 hours ago, tater said:

 

Somehow missed these:

 

 

Big green flash on the startup. 

Any idea why? 

[Rutabaga22]

31 minutes ago, JoeSchmuckatelli said:

Big green flash on the startup. 

Any idea why? 

It's a certain gas, I don't remember what tho.

[tater]

TEA-TEB

triethylaluminum-triethylborane

[JoeSchmuckatelli]

1 hour ago, tater said:

triethylaluminum-triethylborane

Hmmmm... None of those words are "copper". 

Shows how much I remember from Freshman Chem! 

[tater]

The triethylborane burns green.

[StrandedonEarth]

Same “starter fluid” used on F9s

[mikegarrison]

11 minutes ago, StrandedonEarth said:

Same “starter fluid” used on F9s

TEB was also used to start the afterburners of the SR-71. That was one of the things that limited the endurance of those planes. They only had just so many afterburner restarts per flight, and once they were out, they were out.

[sevenperforce]

Interesting that they're using TEA-TEB for a hydrolox engine. Ordinarily you can just use an augmented spark igniter because hydrogen ignites so easily. I wonder if they're going with a hypergolic starter because it ends up being simply lighter for a bunch of different engines, or if they're doing a hypergolic start now but something else in the future.

It was interesting to me that the Ars Technica article didn't talk about it being an aerospike. It may not be exactly an aerospike after all.

Quote

"Because all parts of a rocket are designed to be as light as possible, such extended nozzles are often fairly fragile because they're only exposed above Earth's atmosphere. So one problem with getting an upper stage back from Earth [orbit] . . . is protecting this large nozzle. One way to do that is to bury the engine nozzle in a large heat shield, but that would require more structure and mass. . . . [D]uring reentry, with a smaller number of smaller thrusters firing, it's easier to protect the nozzles.

"What you're seeing in the photos of the test is a high-performance upper-stage engine that can operate within atmosphere at deep throttle to support vertical landing but then also perform at a higher ISP than some variants of the RL 10 engine in space."

Higher than some RL-10 variants -- that's quite the boast!

It sounds less like a proper aerospike and more like a bimodal engine that operates as an aerospike at low throttle but as a fully-expanded vacuum engine at high throttle.

The patent may prove instructive:

Quote

In the patent disclosures: "Referring to FIGS. 7 and 8, the augmented aerospike nozzle 10 includes at least one initial nozzle portion 60 through which exhaust gas initially exits at least one high pressure chamber 36, and a secondary nozzle portion 62 downstream relative to the initial nozzle portion 60. . . . The secondary nozzle portion 62 also includes an outer expansion surface 30 outboard of the inner expansion surface 26, and an expansion cavity 32 defined between the inner expansion surface 26 and the outer expansion surface 30. Referring to FIG. 7, in some embodiments . . . [a]n inflection point 68 is defined where the outer diverging surface 66 of the initial nozzle portion 60 meets the outer expansion surface 30 of the secondary nozzle portion 62."

In other words: at low throttle for landing, there is induced flow separation at the inflection point 68, making the entire engine act as a conventional aerospike. However, at high throttle, the inflection point 68 acts like a secondary throat and is the origination point for the bulk of expansion, allowing the entire cavity to serve as an expansion nozzle without any aerospike effects required. As envisioned by FIG. 8, it is even possible that no outer expansion surface 66 is required at all, allowing the inflection point and the nozzle throat to be one and the same.

It also appears that the inflection point 68 may also be the gas bellows seal at the gimbal joint.

[wumpus]

On 10/10/2022 at 6:43 PM, mikegarrison said:

TEB was also used to start the afterburners of the SR-71. That was one of the things that limited the endurance of those planes. They only had just so many afterburner restarts per flight, and once they were out, they were out.

In other words, you could refuel in air, but you couldn't refill your TEB.  And you can't refuel with afterburners running.

[mikegarrison]

1 hour ago, wumpus said:

In other words, you could refuel in air, but you couldn't refill your TEB.  And you can't refuel with afterburners running.

Yes.

The interesting thing is that as the airplane refueled it got heavier, and toward the end of refueling they didn't have enough thrust to stay in level cruise. But two engines on afterburner would have been too much thrust. So they would would put one engine on afterburner and deal with the asymmetric thrust by side-slipping.

[sevenperforce]

7 minutes ago, mikegarrison said:

The interesting thing is that as the airplane refueled it got heavier, and toward the end of refueling they didn't have enough thrust to stay in level cruise. But two engines on afterburner would have been too much thrust. So they would would put one engine on afterburner and deal with the asymmetric thrust by side-slipping.

Was literally typing this out.

The SR-71 could not achieve supersonic flight on its engines alone without afterburners, but once through the transonic regime, it could shut off the afterburners and cruise just fine at around Mach 1.2 with military power.

However it was actually more efficient in ramjet mode with full afterburner at Mach 2++. The ramjet inlets were designed for Mach 3.24 so that's where they flew the "cleanest" and that was usually the target "top speed" for sorties.

Purportedly it got to over Mach 3.5 on a few occasions.

[mikegarrison]

7 minutes ago, sevenperforce said:

Was literally typing this out.

The SR-71 could not achieve supersonic flight on its engines alone without afterburners, but once through the transonic regime, it could shut off the afterburners and cruise just fine at around Mach 1.2 with military power.

However it was actually more efficient in ramjet mode with full afterburner at Mach 2++. The ramjet inlets were designed for Mach 3.24 so that's where they flew the "cleanest" and that was usually the target "top speed" for sorties.

Purportedly it got to over Mach 3.5 on a few occasions.

The engine and inlet were totally unique and quite clever.

The inlet had a bunch of operating modes controlled by how far the center spike was pushed forward or pulled back, allowing it to handle anything from subsonic to Mach 3+.

The airflow was then either sent through the core, dumped as pure bypass, or routed around the core to the afterburner. At high Mach numbers, the core was actually producing negative thrust, so they routed almost all the air around the core and burned it in the afterburner as a ramjet.

All this was done without using digital computers.

[tater]

I recall reading that it leaked like a sieve on the ground until it heated up in flight. (unless I am misremembering)

[sevenperforce]

6 minutes ago, tater said:

I recall reading that it leaked like a sieve on the ground until it heated up in flight. (unless I am misremembering)

Yes, in order to keep the tanks from buckling under thermal expansion during flight, there were big gaps that left it leaking on the ground.

It also had to refuel immediately after takeoff, but this was not because of leaks; the volume of leaked fuel was negligible. Rather, it could not take off with a full fuel load at all, even with both afterburners. So it would take off with a partial fuel load and rendezvous with a specially modified tanker for top-off. Even then, it would eventually become too heavy to sustain level flight and would need to fire up a single off-axis afterburner to hold altitude and complete the fuel transfer.

Most tanker refueling runs are performed at or around cruising speed but the tanker had to get all the way up to its max speed of ~500 knots to keep pace with the Blackbird.

[tater]

What an epic aircraft.

[JoeSchmuckatelli]

19 hours ago, tater said:

What an epic aircraft.

This whole exchange suggests that beyond just being an epic aircraft, the crews and support people who kept it flying were epic.  (If you typed that up as a 'plan' beforehand, I doubt such would ever be approved.  The fact is, people are amazing - and if they want something badly enough, they'll figure out how to make it happen!)

[sevenperforce]

Here's a fantastic video showing late night prep and takeoff.

Note you can see fuel visibly leaking at 2:25 and following.

Spectacular afterburner ignition at 11:10.

 

[sevenperforce]

One of the wildest things ever done with an SR-71 (which brings this thread back from its brief derailment) was to flight-test one of NASA's aerospike engine designs.

Here's the hydrolox linear aerospike on the ground:

And here's what it looked like when it was mounted to the back of the SR-71:

Sadly there are no images of it being fired in flight.

[magnemoe]

On 10/13/2022 at 5:02 PM, JoeSchmuckatelli said:

This whole exchange suggests that beyond just being an epic aircraft, the crews and support people who kept it flying were epic.  (If you typed that up as a 'plan' beforehand, I doubt such would ever be approved.  The fact is, people are amazing - and if they want something badly enough, they'll figure out how to make it happen!)

Yes, fact like plane leak fuel standing on the runway before takeoff, has to use one engine on afterburner during in flight refueling in an two engine plane with engines far from the center line(much less an issue on a F-15  ) is stuff you don't want to read in project plans. 

As I understand the U2 is also an very hard plane to fly, not to talk about landing. 

But the SR-71 is a so beautiful plane, entire thing screams speed. 
 

Edited October 15, 2022 by magnemoe

[JoeSchmuckatelli]

1 hour ago, magnemoe said:

SR-71 is a so beautiful plane

Possibly one of the most beautiful and iconic! 

[sevenperforce]

Back to the OP, we had a new engine test over Thanksgiving:

Lovely Mach diamonds. I'm guessing that this is still a low-throttle test. Those plumes are extremely orange, which suggests low combustion temperatures and a lot of molecular hydrogen burning in the ambient air.

[tater]