Princeton University attempt at a suborbital space shot?

Not sure why I can't edit previous posts, but upon further analysis, performance may not have been what we expected due to some coning during the second stage burn. Further analysis is warranted but nothing is official until the press release comes out.

Thanks for keeping us in the loop .

Some new technical documents were uploaded to the Princeton SpaceShot documentation page:

https://rockets.princeton.edu/spaceshot-technical-documentation

Bob Clark

Great video here describing the USC teams flight to the 100 km von Karman line for suborbital space:

https://mach5lowdown.com/2019/07/13/space-or-nothing-first-student-launch-to-space/

I like the last line shown on screen in the video:

“With its founding goal complete, the lab has set its sights even further now that the sky is no longer the limit.”

Bob Clark

Spotted in the wild last night.

Cool!
And, congratulations to you too, Dr. Reese.

Congratulations to all involved!

An amateur rockoon to suborbital space?

A rockoon is a rocket that is first lofted to high altitude by balloon then ignited to reach suborbit or orbit.

It has been accomplished by the military though not by amateurs to reach suborbit. Stanford University has done it to relatively lower altitude of max. 45,000 feet with the ignition at 30,000 feet:



Purdue has planned to attempt it as well:



However, amateur balloons lofted by students have reached to 100,000 feet, ca. 30 km. If it were possible to launch a rocket at that altitude then virtually any COTS (commercial off the shelf) APCP rocket loftable by the balloon could then reach suborbital altitude when launched from the balloon.

For the mass ratio of a commercial APCP rockets is commonly 2.5 and above and the ISP commonly 200s or so, the delta-v possible by the rocket equation would be 200*9.81*Ln(2.5) = 1,800 m/s. The gravity loss being 9.81 times the burn time would be comparatively low since the burn time for amateur rockets is only a few seconds.

IF we can discount air drag, the additional altitude reached is then (d) = v^2/(2*g) = 165 km, for a total of 195 km.

However, the disregarding of the air drag is why the launch would have to be at high altitude for this to work. At 100,000 feet the air density is about 1/100th that at sea level and with the rocket rapidly achieving higher altitude and with air density dropping exponentially, the air drag is reduced even further.

The key problem though is the ignition at high altitude. This has been a problem with amateurs attempting suborbit with staged rockets, the upper stage doesn’t ignite. Two issues that need to be solved are the very low air density and extreme cold at that altitude, well below freezing.

So a proposal: enclose the rocket inside the helium balloon. This solves the low density problem. For the cold temperature issue, there are two remedies we could apply. First, use heated helium and secondly, use a dark colored balloon material so it could be warmed by the Sun on ascent.

Note that “solar balloons” using dark colored material can raise to altitude just filled with air like hot air balloons do, only simply heated by the Sun.

Bob Clark

It wasn't clear to me from the video whether the Purdue students were trying for orbital or suborbital flights. I suppose one would naturally come from the other. You do see the real challenge of guidance from both videos. In the Stanford one, the rocket launched from the balloon appears to fly a spiral pattern based on the smoke trail (~1:50). I suppose that makes sense--the typical 50 ft/s launch rail exit velocity assumes you have sea-level-ish air to work on the fins. The Purdue launch rig jumps significantly when the rocket is launched (~1:00), and that's with it staked to the ground. Also, why was Stanford estimating altitude to 40K based on video and rocket equations? Both altimeters and GPS would be fine in that altitude.

High altitude ignition is a challenge that many here have largely solved. If students ask for help/advice...

A helium balloon of the type used for high altitude is not pressurized.
The ignition problems are because hobby igniters are used rather than one that is properly designed for the application and the motor has burst disc.

RGClark said:

So a proposal: enclose the rocket inside the helium balloon. This solves the low density problem.

Click to expand...

How? Balloons get their lift by being less dense than the surrounding air.

Honestly, the more you look into rockoons the more marginally appealing they look. Don’t get me wrong, I’d love to do one someday, but the logistics are even harder than technical problems like ignition.

Basically, for the most part forget about launching one from US land. Instead, you are most likely going to have to launch and recover from international water.

While the balloon isn’t too bad for a 1200, 1600, or 3,000 gram balloon, helium would be very fairly expensive and while hydrogen is usable and cheap, I’m not sure if I’d want to try wrangling it on a boat.

Worse of all, unless you get a free boat access, boat rentals are expensive! Also, recover in the ocean could be challenging and damaging to components.

Launching from a balloon also presents some fairly major stability problems. Many rockets launched from 70,000 feet had incredibly high acceleration, large fins and still needed a decently large launch tower. While this is hardly impossible for amateurs and especially for research motors, this adds to the difficulty, weight and this cost.

I think it would be cool to use pyrotechnically pre-spun rockets at closer to 100,000 feet, but there are design issues with roll-coupling, balancing and the like that would need some engineering work to overcome.

Finally, balloons tend to have some stability problems and the solutions tend to add further weight and complexity.

In my analysis, unless you are planning on launching about four or more tiny rockets to briefly poke above 100km with a negligible payload it is cheaper to go with a well optimized 2 stage research rocket.

Also, rockoons have more limited and difficult scaling then a more conventional multi-stage rocket. Ultimately, I think that rockoons are fascinating, but for an amateur space shot only make sense if you already own or have a friend who owns an oceangoing boat and is willing to let you use it for cheap.

UhClem said:

How? Balloons get their lift by being less dense than the surrounding air.

Click to expand...

Yes. The helium is less dense than the surrounding air that is why it rises. However, a problem is that as the balloon rises the surrounding air becomes less dense and the balloon expands as the pressure inside equalizes to the pressure outside. This will be bad for this scenario because we want the pressure inside to remain near sea level.

What would be required is a stronger or thicker material than commonly used for helium balloons so the balloon remains at the same volume and the same internal pressure. This stronger or thicker material will be heavier so less payload can be lofted.

Bob Clark

That won't work either.
Air at 100,000' is way less dense than hydrogen or helium at sea level

MClark said:

A helium balloon of the type used for high altitude is not pressurized.
The ignition problems are because hobby igniters are used rather than one that is properly designed for the application and the motor has burst disc.

Click to expand...

Yes. But my understanding is the igniters used by professional rocket scientists to insure high altitude ignition are of a dangerous type or even ITAR controlled.

Robert Clark

RGClark said:

Yes. The helium is less dense than the surrounding air that is why it rises. However, a problem is that as the balloon rises the surrounding air becomes less dense and the balloon expands as the pressure inside equalizes to the pressure outside. This will be bad for this scenario because we want the pressure inside to remain near sea level.

What would be required is a stronger or thicker material than commonly used for helium balloons so the balloon remains at the same volume and the same internal pressure. This stronger or thicker material will be heavier so less payload can be lofted.

Bob Clark

Click to expand...

No, you don’t want the pressure within the balloon to remain near sea level. That alone would limit the altitude you could achieve.

RGClark said:

Yes. But my understanding is the igniters used by professional rocket scientists to insure high altitude ignition are of a dangerous type or even ITAR controlled.

Robert Clark

Click to expand...

Bob, haven't seen you in a while. Things that catch on fire are to be respected of course ; and iron or sulfur are in certain small sizes are on the ITAR lists. Ignition at altitude is not especially exotic.

Steve Shannon said:

No, you don’t want the pressure within the balloon to remain near sea level. That alone would limit the altitude you could achieve.

Click to expand...

Steve Shannon said:

No, you don’t want the pressure within the balloon to remain near sea level. That alone would limit the altitude you could achieve.

Click to expand...

A valid point. How high have amateurs being able to ignite upper stages using standard sea level igniters? Jim Jarvis has ignited an upper stage on ThreeCarbYen at 40,000 feet using BKNO3. I’m looking for ways of doing it without using BKNO3 or thermite to ignite the upper stages at high altitude.

Here’s an article on the Stanford University rockoon launch:

FEBRUARY 1, 2015
Launching a rocket from a high-altitude balloon
Two Stanford aerospace majors won a research grant to push the limits of amateur high-altitude exploration using a scientific balloon and a custom-designed rocket.
Cox said one of the project’s key successes was the development and deployment of the mechanical launch system, which went through several iterations.
“The final solution, a pressured tube that utilized a centuries-old technique originally developed for cannons – the ‘sabot’ – allowed us to achieve a stable exit of the rocket from the balloon portion of the vehicle using a very small launcher,” he said.
Cox said the final launch – on Jan. 3, 2014, in Kern County, California – was a success. The rocket launched at 30,000 feet and soared to approximately 45,000 feet. All systems checked out perfectly.
https://news.stanford.edu/2015/02/01/launching-rocket-high-altitude-balloon/

The article only mentions that a pressurized tube being used to achieve stable exit from the balloon. However, it may also have allowed reliable ignition at that high altitude. It would be interesting to find out the answer to that question.

If using a pressurized tube would work, then this would also work for ignition of upper stages on multistage rockets not using ballon launch. For instance, for rockets intended for orbital launch.

Bob Clark

dhbarr said:

Bob, haven't seen you in a while. Things that catch on fire are to be respected of course ; and iron or sulfur are in certain small sizes are on the ITAR lists. Ignition at altitude is not especially exotic.

Click to expand...

Recently, I’ve been thinking of launch methods that actually don’t use any chemical propulsion at all, specifically, using stored mechanical energy of motion like with flywheels.

Bob Clark

Steve Shannon said:

No, you don’t want the pressure within the balloon to remain near sea level. That alone would limit the altitude you could achieve.

Click to expand...

Found this comment of yours while searching on the forum for airstart methods:

_______________________________________________________
Nov 9, 2018 #54
Steve Shannon
Is it really possible to accomplish that with HEI systems? I can't quite wrap my head around how you'd assemble a motor using HEI without having the igniter/ignition system in place. For a second I thought the unit Tony linked to earlier would be install-able in the field after motor assembly but after looking at the pictures I'm not quite sure.
You’ve hit the nail on the head. It’s simply not possible with any existing amateur head end ignition system to install the initiator after the motor is in the rocket and the rocket is on the pad and pointed in a safe direction. The RCS/Aerotech head end system (the one Tony referenced) at least allows the motor to be fully assembled before inserting the head end initiator.
That’s also the problem with all traditional multiple stage amateur rocket vehicles. The booster is the only stage which allows the initiator to be installed after the entire rocket is assembled, on the pad, and pointing in a safe direction.
That’s the problem that should be solved before working on how to make air starts more reliable.
This obviously doesn’t apply to parallel staged rockets where all of the initiators can be installed on the pad.
_______________________________________________________
https://www.rocketryforum.com/threa...lty-with-airstarts.148953/page-2#post-1830143

Perhaps parallel staging could be used to solve the problem of high altitude ignition. You could use side rockets that ignite on the ground around a central rocket that doesn’t ignite until after the side rockets jettison.

This would solve the issue of how to safely install a head end igniter.

Alternatively, you could have also the central rocket ignite at the same time as the side rockets. BUT the central rocket would be given a very slow burning propellant formation so that it burns even after the side rockets have finished burning and are jettisoned. Ideally it would be arranged to burn slowly at first then more rapidly after the side rockets jettison.

Bob Clark

Honestly, why not use V-BKNO3? I recently started using it and it has been an absolute joy to work with. Reliable ignition in under 100ms every time (usually about 40ms), durable, relatively safe, affordable and not even all that hard to make. I think that apogee sells it as a kit. There’s a reason the pros use it after all.

As for rockoon stability, the things I have considered are:

1. Aerodynamic stabilization. Traditional way is to use a high acceleration motor (often over 100+ g), large fins, shortish launch tower ignited at 70,000 feet. It’s the traditional way to do things, still a decent amount of drag at those heights. Can do single-stage but might be worth doing two.

I consider the pressurized tube to be a variant of the launch tower that allows lower-acceleration motors to be used to be used at a cost of a bit of additional weight and engineering. Often it would be a worthwhile tradeoff and can be modified to help keep the engine insulated on the way up.

I think that tower + high acceleration motor + large fins at 70,000 feet is an amateur’s best bet. It still will require engineering and addressing problems such as how well do motors do at lower temperatures, the ignition problem (I’d suggest using a well-sized V-BKNO3 igniter), minimizing sway under the ballon and finding a place to launch, but it sure would be cool!

2. Spin-stabilization. Can work at higher altitudes and be spin up using two smaller rocket motors or an electric motor. Overall greater mass efficiency, but requires more careful booster design to avoid things like inertial roll coupling and will probably require spin-balancing.

3. Active stabilization. Interesting, but very complex and makes it very difficult to get an adequate mass ratio on a rocket using commercial hardware. While cool, I consider this the least practical method.

RGClark said:

Found this comment of yours while searching on the forum for airstart methods:

_______________________________________________________
Nov 9, 2018 #54
Steve Shannon
Is it really possible to accomplish that with HEI systems? I can't quite wrap my head around how you'd assemble a motor using HEI without having the igniter/ignition system in place. For a second I thought the unit Tony linked to earlier would be install-able in the field after motor assembly but after looking at the pictures I'm not quite sure.
You’ve hit the nail on the head. It’s simply not possible with any existing amateur head end ignition system to install the initiator after the motor is in the rocket and the rocket is on the pad and pointed in a safe direction. The RCS/Aerotech head end system (the one Tony referenced) at least allows the motor to be fully assembled before inserting the head end initiator.
That’s also the problem with all traditional multiple stage amateur rocket vehicles. The booster is the only stage which allows the initiator to be installed after the entire rocket is assembled, on the pad, and pointing in a safe direction.
That’s the problem that should be solved before working on how to make air starts more reliable.
This obviously doesn’t apply to parallel staged rockets where all of the initiators can be installed on the pad.
_______________________________________________________
https://www.rocketryforum.com/threa...lty-with-airstarts.148953/page-2#post-1830143

Perhaps parallel staging could be used to solve the problem of high altitude ignition. You could use side rockets that ignite on the ground around a central rocket that doesn’t ignite until after the side rockets jettison.

This would solve the issue of how to safely install a head end igniter.

Alternatively, you could have also the central rocket ignite at the same time as the side rockets. BUT the central rocket would be given a very slow burning propellant formation so that it burns even after the side rockets have finished burning and are jettisoned. Ideally it would be arranged to burn slowly at first then more rapidly after the side rockets jettison.

Bob Clark

Click to expand...

One basic safety related rule of thumb when clustering is to have any central motors overwhelm any motors that are mounted well off center in order to get a good stable vertical flight. For that reason we would prefer not having low average thrust central motors.

Steve Shannon said:

No, you don’t want the pressure within the balloon to remain near sea level. That alone would limit the altitude you could achieve.

Click to expand...

In case anybody is interested: The primary killer of the scheme appears to be the mass of the balloon itself, which is quite heavier than the compressed gas within it. A balloon strong enough to maintain sea level pressure inside of it will be heavy. If it is made of Mylar (1.38g/cm^3, 210 MPa) and filled with hydrogen the achievable altitude is in the neighborhood of 17kft. That is with zero payload.
Even a Sci-Fi balloon made out of graphene and filled with monatomic hydrogen ends up being limited to about 85ft, again without any payload (this one is mostly limited by the compressed gas).

Disclaimer: I'm not exactly a certified spherical pressure vessel calculationeer and also made some lazy assumptions about the gasses.

Reinhard

Rocket501 said:

Honestly, why not use V-BKNO3? I recently started using it and it has been an absolute joy to work with. Reliable ignition in under 100ms every time (usually about 40ms), durable, relatively safe, affordable and not even all that hard to make. I think that apogee sells it as a kit. There’s a reason the pros use it after all.

Click to expand...

I’m looking at this from the aspect that suborbital launch and even orbital launch is an achievement that most student university engineering labs can accomplish. From what has been said on this forum on BKNO3 and thermite, I’m not sure that can be done safely, uniformly, if it were done for large numbers of different student groups.

For experienced, independent amateurs that have done high power launch multiple times I can see it being used. I’m not so sanguine about it being used by student groups.


Bob Clark

RGClark said:

For experienced, independent amateurs that have done high power launch multiple times I can see it being used. I’m not so sanguine about it being used by student groups.

Click to expand...

A student group must gain knowledge and experience before attempting any rocket flight requiring advanced technology. The technology needed for a Space shot (nonetheless orbital) is not accessible to most mentors or industry professionals; many with some experience are unwilling to take the time and accept the risk to help a student team.

So, over time and multiple generations of student teams, the college group institutionally has to advance and retain the same level as an "experienced, independent amateur". USC is the best example of this.

Specific to your assertion, the technology background for high-altitude ignition is available in the general literature with some searching. For U.S. persons, BKNO3+Viton is available for purchase (thermite should not be used at all). The implementation specifics are learned through research, design, and testing. No shortcuts.

Regarding rockoon flights, ignition is a minor problem compared to the logistics and authorization. International waters does not exempt a U.S. group from the FAA regulations. (I've explained many of the challenges before when the topic has been brought up. I used to work here: https://www.csbf.nasa.gov/ ). Several start-up companies and amateur groups have learned over the years that a rocket under a balloon only seems easier/better until you work through the details. A "big dumb booster" is cheaper, safer, easier logistically, and at least possible to get FAA/AST approval compared to a rockoon.

Stanford rocketry group is continuing to work towards a rockoon:

Air-Launched. Low-SWaP, Space-Capable Sounding Rocket.
Publisher: IEEE
15 Author(s)
Anjali Roychowdhury ...
Abstract:
With the goal of being the first civilian university to reach space, The Stanford Student Space Initiative's Spaceshot Team (SSI Spaceshot) has designed a custom rocket-balloon (rockoon) system to achieve an apogee height of greater than 100 km (i.e. to cross the Kármán Line, a widely-accepted definition of the boundary of space), while demonstrating a cheap, low Size, Weight, and Power (SWaP), suborbital launch technology. Suborbital launch represents a high-potential space for growth in aerospace as it provides a high-value market for aerospace research and a low-cost, lower-risk opportunity for agents with less capital to access space. Technologies such as this open-source rocket-balloon system provide an incredible opportunity to democratize space and provide access to aerospace to all. Leveraging the experience of an international-award-winning rockets team, a world-record-breaking high-altitude balloon team, and members who have built satellites, high-voltage DNA synthesizers, and more, SSI is building an integrated rocket-balloon system. The system consists of a zero-pressure balloon platform which will carry a 20 kg rocket with a commercial-off-the-shelf motor to 27 km. At that height, the rocket will launch to reach a final expected apogee of 125 km. Although the underlying architecture has been verified and tested for decades, from NASA to modern space startups, SSI's design is heavily optimized to be low SWaP, affordable, and accessible as an open-source platform. In the process of creating an efficient, effective design in this problem space, SSI has created custom composites designed for the hypersonic thermal load, designed robust payload bays to survive high-shock, and investigated different stability methods for high-altitude, low-atmospheric-density launches. This project hopes to advance the emerging field of accessible aerospace by publishing our simple and achievable design for suborbital launch technology.
Published in: 2019 IEEE Aerospace Conference
Date of Conference: 2-9 March 2019
https://ieeexplore.ieee.org/abstract/document/8741861

Unfortunately, the report is behind a paywall so I don’t know the method they are using to insure high altitude ignition.

Bob Clark

RGClark said:

Stanford rocketry group is continuing to work towards a rockoon:

Air-Launched. Low-SWaP, Space-Capable Sounding Rocket.
Publisher: IEEE
15 Author(s)
Anjali Roychowdhury ...
Abstract:
With the goal of being the first civilian university to reach space, The Stanford Student Space Initiative's Spaceshot Team (SSI Spaceshot) has designed a custom rocket-balloon (rockoon) system to achieve an apogee height of greater than 100 km (i.e. to cross the Kármán Line, a widely-accepted definition of the boundary of space), while demonstrating a cheap, low Size, Weight, and Power (SWaP), suborbital launch technology. Suborbital launch represents a high-potential space for growth in aerospace as it provides a high-value market for aerospace research and a low-cost, lower-risk opportunity for agents with less capital to access space. Technologies such as this open-source rocket-balloon system provide an incredible opportunity to democratize space and provide access to aerospace to all. Leveraging the experience of an international-award-winning rockets team, a world-record-breaking high-altitude balloon team, and members who have built satellites, high-voltage DNA synthesizers, and more, SSI is building an integrated rocket-balloon system. The system consists of a zero-pressure balloon platform which will carry a 20 kg rocket with a commercial-off-the-shelf motor to 27 km. At that height, the rocket will launch to reach a final expected apogee of 125 km. Although the underlying architecture has been verified and tested for decades, from NASA to modern space startups, SSI's design is heavily optimized to be low SWaP, affordable, and accessible as an open-source platform. In the process of creating an efficient, effective design in this problem space, SSI has created custom composites designed for the hypersonic thermal load, designed robust payload bays to survive high-shock, and investigated different stability methods for high-altitude, low-atmospheric-density launches. This project hopes to advance the emerging field of accessible aerospace by publishing our simple and achievable design for suborbital launch technology.
Published in: 2019 IEEE Aerospace Conference
Date of Conference: 2-9 March 2019
https://ieeexplore.ieee.org/abstract/document/8741861

Unfortunately, the report is behind a paywall so I don’t know the method they are using to insure high altitude ignition.

Bob Clark

Click to expand...

As a student, I can read the article for free. The article has no mention of ignition systems. The motor they were planning on using is a Cesaroni N5800 with either a motor spin-up or CO2 spin-up to about 10Hz. They were planning on launching with a 20kg all-up platform weight at an altitude of 26 (or 27) km. The article had quite a few questionable statements and overall seemed to be of questionable practicality. Also, the internal project deadline was July 20th, 2019 so either the schedule has slipped (quite possible) or they abandoned it (ditto). The whole statement is pretty high-level not bothering to go into overmuch detail about weight breakdown and the other specific engineering details.

The whole right up about the recovery was confusing. The planned recovery system weight was only 2kg which is rather optimistic, but not impossible. They noted the difficulty in using blackpowder in a space environment, so their plan was to instead deploy a drogue or streamer at an altitude of 8km and the main at "about 150m (1500 feet)" and 73 m/s which seems to be leaving things a bit tight even if they mean the higher number. It's a tad weird that on a paper with 15 authors nobody consider that there is a rather big difference between 150m and 1500 feet.

Notably, the article doesn't really talk much about getting regulatory permission, even if it does consider dispersion on both ascent, launch and recovery (I approve of this) and always maintaining positive command link (ditto) with angle lockout, but even then, I think the FAA would be extremely leery about letting it be launched over the CONUS.

Is Stanford prohibited from using research motors by their university?

I’m not a Stanford student (full disclosure, I go to their rival school, UC Berkeley), but I believe they are allowed to use research motors, they just wanted to minimize risk, which does make sense.

Thank you. Standing by for a response to confirm from Stanford.
LOL when I thought of putting a HP rocket on a balloon to minimize risk. ;-)
I believe it's a problem when the primary goal is to reach space and not something like being creative and perhaps a bit more all-inclusive with what other students may find more interesting. I see this btw when I speak with students that have other interests other than "going to space" but go along with the group; Which is driven by a few students. So, for example, rather than spend a lot of money and time reinventing a LR-101, they could be creating a new 3D printed turbo pump design. Or, a couple of groups doing different things.

Even the balloon rocket thing is like 50 years old news. And, I read their statement suggesting an emerging technology, and I don't think there's any future for balloons launching rockets. There would be a lot more interest in say, launching a rocket from a high alt UAV.

As students, I would think that you would want experiences that would look good at the interview. Do you think these large aerospace companies don't know how to go to space? I would think some creative thinking and building would be a lot more appealing and allow more students to have an active involvement.
Yeah, I believe we are probably at least partially to blame. We are a bunch of altitude-speed junkies. Most people when they get started with rocketry as a hobby immediately start focusing on reaching space. Just wish the line was a bit lower!
Does TRA have an award for the most creative student project? How about AIAA?