Author Topic: Stratospheric-Airship-Assisted Orbital Payload Launching System  (Read 8598 times)

Offline IRobot

  • Full Member
  • ****
  • Posts: 1174
  • Portugal & Germany
  • Liked: 210
  • Likes Given: 197
This starts to sound like the 25km high pyramid thread from 2 years ago...
Minimum advantage for a lot of trouble. Keep it simple!

Offline saaopl

  • Member
  • Posts: 14
  • Washington DC
  • Liked: 0
  • Likes Given: 0

I actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.
http://saaopl.net/index.php/features/

One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.

Actually, if you'll read the quote above from Musk it doesn't mention reusability at all.  Musk's point is valid even if you have full reusability.

Musk's point is that an aircraft-launched system essentially makes the aircraft an additional stage.  You have all the cost and complexity of an additional stage, but it's an additional stage that gives you much less benefit than a rocket stage.  The same is true for an airship-assisted launch system -- the airship is an additional stage, but one that gives you much less benefit than a rocket first stage.

You didn't address this point in your reply.


The cost and complexity of designing and constructing an airplane and an airship are at different level. The launch platform used in SAAOPL system can be much simpler than a conventional HAA at the same level. Structurally, it is a mix of an airship and balloon, with the maximum speed close to 40m/s at approximate 22km altitude, which is substantially lower than the maximum airplane speed of 200+ m/s at 10km. This difference alone already can save a lot of aerodynamic complexities.

Another thing to be emphasized that SAAOPL is an unconventional launching system. It is not a wisdom choice to isolate each components in the system and compare with conventional stages individually, rather than comparing systems as a whole. Taking the launch platform for example, if simply comparing it with conventional first stage in the scenario of launching an conventional upper stage, it doesn't worth at all, since it adds zero delta-V, lifts very limited altitude and doesn't boost reliability.  However, within SAAOPL system, the launch platform brings SLSS out of dense part of atmosphere (significantly boost the performance of SLSS), and provide the crucial altitude redundancy that SLSS needs to dump its fuel in the scenario of immediately-after-launch engine failure.

As a novel system, delivering a cargo to space orbit using SAAOPL system conceptually can be like sending a cargo to another continent using Boeing 747. The design of SAAOPL system have placed reusability, reliability and short-launch cycle in the key positions since the beginning.
« Last Edit: 04/18/2017 01:31 AM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 3534
  • Sunnyvale, CA
  • Liked: 2101
  • Likes Given: 2477
I actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.
http://saaopl.net/index.php/features/

One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.

Actually, if you'll read the quote above from Musk it doesn't mention reusability at all.  Musk's point is valid even if you have full reusability.

Musk's point is that an aircraft-launched system essentially makes the aircraft an additional stage.  You have all the cost and complexity of an additional stage, but it's an additional stage that gives you much less benefit than a rocket stage.  The same is true for an airship-assisted launch system -- the airship is an additional stage, but one that gives you much less benefit than a rocket first stage.

You didn't address this point in your reply.

The cost and complexity of designing and constructing an airplane and an airship are at different level.

Your airship will need to be quite large, and development of that large airship will be expensive, as will operating it.

The launch platform used in SAAOPL system can be much simpler than a conventional HAA at the same level. Structurally, it is a mix of an airship and balloon, with the maximum speed close to 40m/s at approximate 22km altitude, which is substantially lower than the maximum airplane speed of 200+ m/s at 10km. This difference alone already can save a lot of aerodynamic complexities.

But it introduces other complexities, including a much larger structure and the need to maintain a very large, very lightweight structure.

Another thing to be emphasized that SAAOPL is an unconventional launching system. It is not a wisdom choice to isolate each components in the system and compare with conventional stages individually, rather than comparing systems as a whole.

If you take your SAAOPL system and replace the airship with a conventional rocket stage that is reusable, the system will become much better.  That is a valid criticism of the SAAOPL system.

Taking the launch platform for example, if simply comparing it with conventional first stage in the scenario of launching an conventional upper stage, it doesn't worth at all, since it adds zero delta-V, lifts very limited altitude and doesn't boost reliability.  However, within SAAOPL system, the launch platform brings SLSS out of dense part of atmosphere (significantly boost the performance of SLSS),

So does a conventional rocket first stage.

and provide the crucial altitude redundancy that SLSS needs to dump its fuel in the scenario of immediately-after-launch engine failure.

Many launch systems today have upper stages that cannot abort if the upper stage has a failure after stage separation.  And yet that very rarely causes a problem.  So your SAAOPL system is addressing a potential problem that really isn't important.

As a novel system, delivering a cargo to space orbit using SAAOPL system conceptually can be like sending a cargo to another continent using Boeing 747.

No.  You've provided no reason to consider launching to orbit using an airship as the first stage any more like using a 747 than launching using a Falcon 9.

The design of SAAOPL system have placed reusability, reliability and short-launch cycle in the key positions since the beginning.

So has Falcon 9 and so has Blue Origin's New Glenn.

Placing reusability or any other factor as a goal is meaningless if you make a bad architectural choice, and using an airship as a first stage is a really terrible architectural choice.

Offline saaopl

  • Member
  • Posts: 14
  • Washington DC
  • Liked: 0
  • Likes Given: 0

The cost and complexity of designing and constructing an airplane and an airship are at different level.......



Let's summarize your key points first (Correct me if missed your points):
1 The lauch platform in SAAOPL system is too large. Hence, it should be complex and expensive to build, and hard to maintain.
2 The airship-based launch platform is a worse choice than a conventional rocket first stage even in SAAOPL system.
3 Upper stage rarely failed in previous launch missions. So, it is not worth to consider recovering SLSS.


Feedback:
1 The lauch platform in SAAOPL system is too large. Hence, it should be complex and expensive to build, and hard to maintain.

In a sample implementation that used to investigate and validate the concept of SAAOPL system, yes, the launch platform would be the largest aircraft in history if it is fully expanded at 22.3km altitude. This has been mentioned in previous posts. However, that doesn't mean it is a conceptually complex system, especially comparing with airplane or conventional high-altitude airship.

The largest component of the platform, hydrogen ballonet, is just a pressured streamlined balloon. Given the strength of envelope material is enough, any size of balloon would be possible to be built in a straightforward way: prepare balloon envelope, inflate lifting gas, and that is it.

Regarding to maintenance issue, as mentioned previously, the launch platform is highly lifting-gas-leaking tolerant. Its envelope mostly comprises of structural material, like Zylon, which also can be used for body armor. The conceptual upper limit of single SAAOPL system is approximate 1000-launches/year, which means 4 months continuous usage. As far as I know, material fatigue won't be a serious issue for Zylon if the loading is designed carefully, even taking into account the harsh environment in stratosphere.


2 The airship-based launch platform is a worse choice than a conventional rocket first stage even in SAAOPL system.

The launch platform is designed dedicatedly for SAAOPL. It is able to bring winged-SLSS out of dense portion of atmosphere at a very low speed (Less than 10m/s). If replace it with a conventional first stage that is already supersonic in dense atmosphere (more than 400m/s), how much aerodynamic complexity, dry mass penalty and risk would be added to SLSS and entire SAAOPL system?

Moreover, single SAAOPL system by design has a conceptual launch-frequency upper limit of 1000-launches/year. In such a high-frequency launch schedule, is there any conventional first stage, at least conceptually, can be reused without high risk to failure, without heavy maintenance workload, or even in a failure, the whole system can be survived and the payload can be recovered?


3 Upper stage rarely failed in previous launch missions. So, it is not worth to consider recovering SLSS.

This is simply not true. You might forget the loss of CRS-7 mission not long ago. This is already in a launch frequency much less than the conceptual goal of SAAOPL system. In many cases, the payload is more valuable than launch vehicle itself. In some special cases, so is the launch window.  For example, in Voyager program, if upper stage failed, that lost not only the space probe, but also the launch window once every 175 years. 

In SAAOPL's design, an engine failure of SLSS or other related issues probably just means another launch trial for the recovered payload within 8 hours, using a backup SLSS.
« Last Edit: 04/25/2017 12:03 PM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline saaopl

  • Member
  • Posts: 14
  • Washington DC
  • Liked: 0
  • Likes Given: 0
There will be a presentation dedicated to SAAOPL system in 2017 AIAA SPACE Forum

If you are interested in this novel system and happened to be there, you are more than welcome to come and please feel free to bring your questions.

Session Information:
ST-03, Space Launch and Ground Operations
September 13, 2017 from 11:30 AM to 12:00 PM  in room Celebration 1
« Last Edit: 08/17/2017 01:41 PM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline whitelancer64

How is this better than what DARPA is doing with the XS-1?
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline saaopl

  • Member
  • Posts: 14
  • Washington DC
  • Liked: 0
  • Likes Given: 0
How is this better than what DARPA is doing with the XS-1?

Not very familiar with technical details of XS-1. It seems XS-1 still is a vertical take-off vehicle, like what SpaceX did.

SAAOPL is quite different. It is novel launching system which combines stratospheric launch and HTHL.
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline TrevorMonty

I think your airship concept is great. I'd suggest investigate other markets for your airship that don't involve developing a LV.

Offline Ludus

  • Full Member
  • ****
  • Posts: 866
  • Liked: 323
  • Likes Given: 154
The cost of making a completely novel balloon/dirigible that can lift an orbital rocket is MUCH higher than using an aircraft. Virgin Galactic plans to use an old 747 that comes with a 5th engine mount. They built some of them to be capable of transporting spare engines. A rocket can be suspended under the wing from that mount. Old 747's are coming out of service all the time and are quite cheap compared with building a novel aircraft either like Stratolaunch or lighter than air. Building anything like this that's entirely new is vastly more costly and difficult than putting a used 747 on your AMEX for $15M and having it checked out and modded a bit. By comparison just getting the airship to work would take many years and trials and hundreds of millions of dollars.

You can then put something like Rocket Labs Electron under your wing and you're ready to go.

Virgin and Stratolaunch argue that they can provide flexibility to avoid local weather conditions and can launch to any orbit. They don't claim much gain in mass to orbit from launching in the air.

The math says that lifting a rocket above most of the atmosphere doesn't put it much closer to being in orbit. As other posters have tried to point out, if you could launch your rocket from a 100km tower above the Karman line, technically already in "Space" it wouldn't be very much closer to being in orbit than if you launched it from the ground. That's why Blue Origin or Virgin Galactic's Space Tourism flights aren't even remotely close to putting something in orbit, even though they go into space.

There aren't many numbers provided about the masses involved or the size or lift of the airship. The math says in order for it to put something in orbit, reusable or expendable, the Rocket it carries has to be very nearly the same size as it would have to be if launching from the ground. So the airship or aircraft is basically irrelevant to the calculations. Maybe it has other benefits but making it much easier to launch a payload into orbit isn't one of them. That's Musk's point. Instead of going through all the trouble of developing this airship, you can make the tanks of your rocket a few percent bigger, burn the engines a bit longer and you get the same result. This is true regardless of whether the rocket is reusable or not. It just makes everything even harder if it's intended to be reusable.

Online envy887

  • Senior Member
  • *****
  • Posts: 2766
  • Liked: 1277
  • Likes Given: 804
How is this better than what DARPA is doing with the XS-1?

Not very familiar with technical details of XS-1. It seems XS-1 still is a vertical take-off vehicle, like what SpaceX did.

SAAOPL is quite different. It is novel launching system which combines stratospheric launch and HTHL.

I'd recommend replacing RS-25 with either Merlin or BE-3 because RS-25 cannot do air-start or restart. If it could, Ares I would probably be flying today. XS-1 is ground launched (partly) because of this limitation.

How do you propose to target the booster at a runway after separation? If it cannot restart, it will be limited to launch azimuths that are within it's crossrange capability to a runway, but that still keep the upper stage ground track away from populated areas. This might work for some launch sites and inclinations, but it is a significant limitation that needs analysis.

I'd also recommend doing a detailed analysis to see how much larger the first stage (suborbital spaceship) has to be to do VTHL and put the same upper stage/payload to Mach 12 (por alternatively, what the payload reduction is with the same booster doing VTHL). This will give a mathematical basis for the claim that the balloon "stage" is worth the expense.
« Last Edit: 08/18/2017 01:23 PM by envy887 »

Offline saaopl

  • Member
  • Posts: 14
  • Washington DC
  • Liked: 0
  • Likes Given: 0

I'd recommend replacing RS-25 with either Merlin or BE-3 because RS-25 cannot do air-start or restart. If it could, Ares I would probably be flying today. XS-1 is ground launched (partly) because of this limitation.

How do you propose to target the booster at a runway after separation? If it cannot restart, it will be limited to launch azimuths that are within it's crossrange capability to a runway, but that still keep the upper stage ground track away from populated areas. This might work for some launch sites and inclinations, but it is a significant limitation that needs analysis.

I'd also recommend doing a detailed analysis to see how much larger the first stage (suborbital spaceship) has to be to do VTHL and put the same upper stage/payload to Mach 12 (por alternatively, what the payload reduction is with the same booster doing VTHL). This will give a mathematical basis for the claim that the balloon "stage" is worth the expense.


Stratospheric launch platform (SLP) stables itself in the relative slow and steady airflow in stratosphere. Azimuth and pitch angle of SLP does not necessarily to be same as what are required by stratospheric-launched suborbital shuttle (SLSS). By controling length of tether cables beneath SLP, azimuth and pitch angle of SLSS is set to the predetermined values before separation. SLP also helps SLSS start its engine before separation.

Given the chilly ambient temperature in stratophere, RP-1 is not ideal fuel for SLSS.

Comparing with vertical lift-off rockets, One advantage of SAAOPL system is its reliability. SAAOPL has conceptual goal 1000 launches per year for single SAAOPL system. Hence, engine failure is a scenario that the design of SAAOPL must consider. If engine failure occurs soon after lift-off, both vertical lift-off rocket and its payload will be lost. However,  that would be different for SAAOPL system. If engine failures occurs after being launched from SLP, SLSS has sufficient altitude redundancy, which is provided by SLP, to safely dump all its fuel and glide to an airfield nearby with its payload.
« Last Edit: 08/19/2017 12:03 AM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline TrevorMonty

Most engine failures result in RUD.

Offline saaopl

  • Member
  • Posts: 14
  • Washington DC
  • Liked: 0
  • Likes Given: 0
Most engine failures result in RUD.

That is exactly what the design of SAAOPL system wants to solve. If an engine malfunction was detected, engine can be shut down immediately. SLSS will dump all its fuel into the air and glide back.

Even in the scenario of engine explosion, a layer of Kevlar between engine and SLSS can protect SLSS from serious damage. SLSS and its payload still can be survived and recovered.
« Last Edit: 08/21/2017 01:39 AM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline hkultala

  • Full Member
  • ****
  • Posts: 648
  • Liked: 175
  • Likes Given: 110
Most engine failures result in RUD.

That is exactly what the design of SAAOPL system wants to solve. If an engine malfunction was detected, engine can be shut down immediately. SLSS will dump all its fuel into the air and glide back.

How do you dump it?

The fastest way to dump the propellant of a rocket is with the help of the turbopumps of the engine - by burning it.

Quote
Even in the scenario of engine explosion, a layer of Kevlar between engine and SLSS can protect SLSS from serious damage. SLSS and its payload still can be survived and recovered.

How thick layer? Have you calculated the weight of this? How do your propellant pipes go through this layer?
« Last Edit: 08/21/2017 10:10 PM by hkultala »

Offline hkultala

  • Full Member
  • ****
  • Posts: 648
  • Liked: 175
  • Likes Given: 110
SLP also helps SLSS start its engine before separation.

Little help from SLP is not enough.

https://forum.nasaspaceflight.com/index.php?topic=1958.0

Online envy887

  • Senior Member
  • *****
  • Posts: 2766
  • Liked: 1277
  • Likes Given: 804

I'd recommend replacing RS-25 with either Merlin or BE-3 because RS-25 cannot do air-start or restart. If it could, Ares I would probably be flying today. XS-1 is ground launched (partly) because of this limitation.

How do you propose to target the booster at a runway after separation? If it cannot restart, it will be limited to launch azimuths that are within it's crossrange capability to a runway, but that still keep the upper stage ground track away from populated areas. This might work for some launch sites and inclinations, but it is a significant limitation that needs analysis.

I'd also recommend doing a detailed analysis to see how much larger the first stage (suborbital spaceship) has to be to do VTHL and put the same upper stage/payload to Mach 12 (por alternatively, what the payload reduction is with the same booster doing VTHL). This will give a mathematical basis for the claim that the balloon "stage" is worth the expense.


Stratospheric launch platform (SLP) stables itself in the relative slow and steady airflow in stratosphere. Azimuth and pitch angle of SLP does not necessarily to be same as what are required by stratospheric-launched suborbital shuttle (SLSS). By controling length of tether cables beneath SLP, azimuth and pitch angle of SLSS is set to the predetermined values before separation. SLP also helps SLSS start its engine before separation.

Given the chilly ambient temperature in stratophere, RP-1 is not ideal fuel for SLSS.

Comparing with vertical lift-off rockets, One advantage of SAAOPL system is its reliability. SAAOPL has conceptual goal 1000 launches per year for single SAAOPL system. Hence, engine failure is a scenario that the design of SAAOPL must consider. If engine failure occurs soon after lift-off, both vertical lift-off rocket and its payload will be lost. However,  that would be different for SAAOPL system. If engine failures occurs after being launched from SLP, SLSS has sufficient altitude redundancy, which is provided by SLP, to safely dump all its fuel and glide to an airfield nearby with its payload.

If you use BE-3 or Merlin it can have engine-out redundancy for most of the flight. And you really don't want to start an RS-25 while dangling on cables under a hydrogen balloon... there is a good reason all air-launch vehicle drop first, then fire. The RS-25 is a difficult engine to start even on the ground. If you drop it, there will be times where a abort on the pad is a lot safer. I'd wager the increased risk of the engine not starting and having to abort is greater than the reduction from having abort capability for a small part of the flight trajectory where the vehicle is within gliding range of a runway.

You still haven't clarified how the suborbital booster returns to a runway. There are a very limited number of sites and launch azimuths where both 1) the ground track of the launch trajectory is acceptable and 2) the booster is within gliding range of a runway when it reenters. Most launch locations and azimuths will require a boostback/diversion burn - but RS-25 cannot RESTART, even if you get it to air-start. You could hot-stage, but that adds a whole 'nother set of complications.

RP-1 freezing isn't really an issue, the booster would need insulated tanks anyway - to prevent solid air buildup on the LH2 tanks.

Again, to convince anyone that air-launch is a good idea, you will need to calculate exactly how much booster cost you are saving by adding the expense of a air-lift stage.

Offline Burninate

  • Full Member
  • ****
  • Posts: 1129
  • Liked: 344
  • Likes Given: 72
Aye, the only meaningful advantage of launching from altitude is the ability to use near-vacuum-optimized engines from the start
Are there any advantages to having a much more benign aerodynamic environment (e.g., far lower max Q)?  Would that allow a lighter structure for the actual vehicle, and thus better performance?  If one doesn't have to worry about dense atmosphere, and thus streamlining, does that allow different form factors for the vehicle rather than a slender tube?

There is a fairly large advantage, but only in one area with its own distinct issues: Small launchers.  The smallest launcher that's feasible from the ground is around 10 tons.

Let's give a hypothetical 30 ton 2-stage launcher a 1% payload mass fraction: It can launch 300kg to space.  This isn't very bad - there are satellites in this size range which will pay some money for launch.  Now scale that down by a factor of 10.  A 3 ton 2-stage launcher suffers on a number of metrics that we can fix - Miniaturizing electronics and guidance and comms, a number of metrics that are inherently difficult - working with increasingly thin-walled pressure vessels, and some things we just can't touch - far proportionally greater aerodynamic losses, and thus (because greater aerodynamic force necessitates greater structural strength for the same velocity) a greater mass loss to structural reinforcement, and also a larger dV need & thus wet:dry ratio.  This extends the amount of propellant that needs to be carried, and these effects compound on each other relentlessly.  Long story short: You don't get a 1% payload mass fraction (30kg) out of a 3 ton vehicle of similar design.  Nowhere near.  More likely you'll just never get any kind of payload to orbit.  Somewhere a bit under 10 tons, depending on what tech you use, the aerodynamic-related losses run asymptotic and you just can't make an orbital vehicle that launches from the ground.

You can make one, though, that launches from somewhere above most of the atmosphere.  If you don't have to deal with most of the atmosphere, you never hit the same compounding barriers, and you can scale that 30 ton launcher down to 3 tons without losing all that much payload mass fraction.  You can hypothetically scale things all the way down to launching a single 1U cubesat.

I would note however, that large launchers (EELV class and up) generally don't lose a lot to gravity+drag losses.  The longer the rocket is, the easier it is proportionately to shove through the atmosphere.  So you can't really compete by just using small launchers and upping the volume, without some kind of dramatic advance in mass production.  Alternately, you could find a recurring payload from a paying customer that needs rapid response launches to a number of custom orbits.

But we haven't yet.  And so this sort of idea is not really a feasible business - in a world where there are cheaply reusable first stages and there exist few commercial customers for tiny payloads to custom orbits, a balloon or plane adds so little to the engineering picture that it's difficult to justify those forms of launch.  We're going to be doing mass production of smallsats fairly soon once the LEO comms financing guys feel that launch is cheap enough, but large smallsat dispensers flown from an F9 are likely much cheaper, for a single plane, than custom launches.  Few large constellations will need only one bird per orbital plane.
« Last Edit: 09/04/2017 12:32 AM by Burninate »

Offline aceshigh

  • Full Member
  • ****
  • Posts: 608
  • Liked: 171
  • Likes Given: 16
Firstly, I should put a note here that this is more a conceptual representation than a detailed design.

Secondly, SLSS, as the third word of its name (Suborbital) states,  doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out.

Thanks for your interest and question!

1 - the first time you mentioned SLSS was in this post in reply to mine, so how was I supposed to know it's suborbital?

2 - actually, this is quite confusing, as the other name (your forum nickname) clearly has the word ORBITAL.


3- so, is it ORBITAL or SUBorbital?

4 - if itīs ORBITAL, how can it achieve a 30 km/s delta-v? Fuel tanks seem undersized by an order of magnitude at least.

Offline hkultala

  • Full Member
  • ****
  • Posts: 648
  • Liked: 175
  • Likes Given: 110
Firstly, I should put a note here that this is more a conceptual representation than a detailed design.

Secondly, SLSS, as the third word of its name (Suborbital) states,  doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out.

Thanks for your interest and question!

1 - the first time you mentioned SLSS was in this post in reply to mine, so how was I supposed to know it's suborbital?

2 - actually, this is quite confusing, as the other name (your forum nickname) clearly has the word ORBITAL.


3- so, is it ORBITAL or SUBorbital?

4 - if itīs ORBITAL, how can it achieve a 30 km/s delta-v? Fuel tanks seem undersized by an order of magnitude at least.

Orbital is not 30km/s, it's ~7.8 km/s.

But the tank size is still too small.

Offline aceshigh

  • Full Member
  • ****
  • Posts: 608
  • Liked: 171
  • Likes Given: 16
Yeah, obviously.

Second post in the thread was mine and I asked the same question but wrote 30 thousand km per hour.

I guess I was sleepy when I changed 30k km/h by 30 km/s

Tags: