totm nov 2023 SpaceX Discussion Thread

[Ultimate Steve]

45 minutes ago, sevenperforce said:

• Launch an ASDS-recovery Falcon 9 carrying only an international docking adapter, with a slightly-modified upper stage to allow for boiloff protection and extended restarts, into LEO.

Unfortunately this is where I think your plan would break down. If I read that correctly, you want to restart S2 after you get to the Moon by "light modification." Extra restarts would be easy enough, but insulation for the LOX and insulation (or heaters) for the RP-1 would probably require a bit more than "light" modification. The longest a Falcon has waited before restarting was about six hours, and for the moon it would have to retain fuel for at least 2-3 days (and have enough fuel left ot be useful).

It could be done, but I think you might be stretching the meaning of lightly modified. That would be cool if it happened, though!

[Gkirmathal]

1 hour ago, sevenperforce said:

Propellant transfer on the Falcon upper stage is not really feasible, since the tanks use helium for ullage pressure. I mean, automated high-pressure helium transfer could be done, but it would be an immense, immense redesign.

Orbital docking and upper-stage extended restarts, on the other hand, are definitely feasible.

A Draco-based propulsion assist pallet, mated to the payload adapter inside the D2 trunk, could provide enough dV for the burn out of Lunar orbit and onto an Earth entry trajectory. The same propulsion pallet on a stripped-down D2 could provide enough dV for single-stage ascent off of the moon, though TWR would be insufficient. You'd want to use Joint Lunar Orbit Rendezvous rather than Earth Orbit Rendezvous, though.

I have started crunching the numbers on this, and so the profiles may need to be adjusted slightly depending on dV, but the overall plan is solid.

<snip points 1 to 10>

Those points read like it has to discarded a lot of equipment.

My initial though was: an extended upper stage, a.k. larger volume kerlox fuel tanks + ignition fluids, to give it enough D/v and restarts for both:
1) push "a" payload (D2 + D2 lander version) to it's TLI point, and
2) make it back alone to LEO, to be reused for some next mission.

About the fuel transfer problem, the following idea passed through my head (and I know it sounds rather Kerbal-ish).
Mate two upper stages (designed this purpose, pusher and refueler), docked nose to nose, then tumble them to generate a centrifugal force and use electrical pumps to pump fluids from one upper stage tanks the another? Rinse and repeat until the pusher stage it fueled up.

Then:

• Dock with what ever needs to be delivered from LEO to LLO
• Extended upper stage performs the TLI burn
• Releases payload - the payload does it's own burn to get into LLO to do it's mission
• ExUS adjust orbit, to put it's Pe back into LEO
• At Pe the pusher stage does it's LEO circularization burn
• Refuel etc

About the D2 stages and their reusability. How to go about making th D2 lander, more reusable? That's a thing I was pondering as well.
Might need an orbiting Lunar station for that.

Edited February 16, 2018 by Gkirmathal

[sevenperforce]

15 minutes ago, Ultimate Steve said:

Unfortunately this is where I think your plan would break down. If I read that correctly, you want to restart S2 after you get to the Moon by "light modification." Extra restarts would be easy enough, but insulation for the LOX and insulation (or heaters) for the RP-1 would probably require a bit more than "light" modification. The longest a Falcon has waited before restarting was about six hours, and for the moon it would have to retain fuel for at least 2-3 days (and have enough fuel left ot be useful).

It could be done, but I think you might be stretching the meaning of lightly modified. That would be cool if it happened, though!

The N1's Blok D kerolox upper stage was designed for multiple restarts in cislunar space, back in 1969, so I can't imagine the changes would be TOO extreme. A penguin tumble keeps the propellant together, rather than up against the edge of the stage, for this purpose. Also gives the astronauts a very low simulated gravity to help keep them oriented.

Might need to paint the kerosene tank black to provide solar heating.

11 minutes ago, Gkirmathal said:

Those points read like it has to discarded a lot of equipment.

Yes, you discard some upper stages and some propulsion assist pallets. You also discard your lander. The mission can be flown with a reusable Falcon Heavy if you use a second reusable Falcon Heavy for the TLI and LOI burns, as with Dragon 2.

The above plan does not require Falcon Heavy be man-rated.

11 minutes ago, Gkirmathal said:

My initial though was: an extended upper stage, a.k. larger volume kerlox fuel tanks + ignition fluids, to give it enough D/v and restarts for both:
1) push "a" payload (D2 + D2 lander version) to it's TLI point, and
2) make it back alone to LEO, to be reused for some next mission.

Extending the Falcon upper stage only very marginally increases mass to orbit. In fact, for a fully-expendable Falcon Heavy, you can actually get as much or more payload to orbit by simply going without an upper stage at all. Kerolox doesn't have high enough isp for upper-stage stretches to be rewarding; all the performance of kerolox comes from the early stages.

Unless an upper stage is actually recoverable, then there's no reason to do orbital refueling. Falcon upper stages are expendable. Sending an upper stage back to LEO for reuse doesn't make sense if the only way to refuel it is to send up another expendable stage; just send up the expendable stage in the first place.

11 minutes ago, Gkirmathal said:

About the D2 stages and their reusability. How to go about making th D2 lander, more reusable? That's a thing I was pondering as well.
Might need an orbiting Lunar station for that.

A reusable lander in lunar orbit is dead mass useless unless it can be refueled. Refueling pressure-fed hypergolic tanks on orbit is more or less impossible. So that's the problem there.

A reusable lander would need to have all of its consumables manually replenishable in cislunar space. It would also need to have its entire propulsion system, including RCS, be refuelable.

Dragon 2 is not a good candidate for in-space reuse. Since the hypergolic tanks cannot be refilled in space, the only thing available for reuse is the pressure vessel and ECLSS.

[insert_name]

PAZ got delayed by a day

https://spaceflightnow.com/2018/02/16/falcon-9-paz-mission-status-center/

[Nibb31]

6 hours ago, Elthy said:

Also dont forget ships and planes. Both will pay a lot for good internet...

Ships, planes, and remote locations are niche markets, which is why they are not serviced today by the big operators who are in it for the money.

Servicing niche markets is not going to pay for Mars colonies. If Musk wants to make big money, he will have to go head to head against the established operators for the consumer market, in dozens of countries at the same time.

Not only is that going to cost massive amounts of money to setup business woldwide with shops, support centers, local administration, etc... but you also have to assume that the established telecom industry is going to fight back legally, politically, and economically.

 

[Elthy]

15 minutes ago, Nibb31 said:

remote locations are niche markets

Dpends on what yo call remote. If you count in everyone in Germany with less than 16mbit/s you allready have a few million potential customers, over the world there are propably more than a billion. Since i doubt the constellation will cost more than 10-20 billion dollars its not to hard to imagine this becoming profitable. Its a bold idea, but it could actualy work.

[YNM]

3 hours ago, Green Baron said:

See above :-) Since last year, but only the town.

I bet those optic cables help with the local mobile network !

3 hours ago, Green Baron said:

I have seen people in Africa (East Africa, Tansania, Kenya) run around with black painted cardboxes, playing mobile phone. And many without nothing. In relatively densely populated areas.

Here's a country with crippled currency yet now everyone lives with SMS banking.

I'm well aware that not every single one is like that - Senegal comes to mind, despite being a pretty "rich" country, I've done remittance "research" on it before for other reasons - but it just shows that getting real networks are a lot more sustainable than just getting such weird scheme with rather dwindling market and befuddling side impact with 12,000 lunch boxes on orbit.

And if you still don't have cable, get a protest ! St. Helena gets it better.

[sevenperforce]

55 minutes ago, Gkirmathal said:

Those points read like it has to discarded a lot of equipment.

About the D2 stages and their reusability. How to go about making th D2 lander, more reusable? That's a thing I was pondering as well.
Might need an orbiting Lunar station for that.

More on this....

A reusable lunar lander sounds very good, but without lunar surface assets, it's not necessarily better than an expendable version, in terms of launch costs.

There are two ways of going about it. The first is to make the "moon taxi" 100% reusable. This results in two requirements: first, it needs to be an SSTO, which means it needs to carry almost 4 km/s of dV. That's a lot, especially if you're using hypergolics; you'd need more than 70% of your lander to be propellant. This means pump-fed engines and autogenously pressurized hypergolic tanks, and you need 100% of the propellant to be transferred from Earth, each time. You need to have a way to mate and transfer propellant.

The other way is to use either drop tanks or drop stages. Instead of bringing propellant from Earth, you're bringing either tanks or whole stages, which attach to the lander and are discarded. This no longer requires quite as high a mass ratio, and you may be able to get away with cryogens, but now you have to deal with the problem of orbital assembly, which is different from the problem of orbital propellant transfer. You're also bringing along a specialized set of equipment each time, rather than (perhaps) just a tanker. And that fuel needs to be plumbed to the RCS system as well.

When it all comes down to it, you can probably get a whole new lander into lunar orbit with a lower mass-in-LEO expenditure than doing full reuse.

[softweir]

3 hours ago, Nefrums said:

I still doubt your sources on this. @Green Baron

Where have you gotten this information from? 

According to https://data.worldbank.org/indicator/IT.CEL.SETS.P2 the number of cell phones per person is not that different between most countries any more.

Most cell users in Africa use very basic, 2G models. If they want to know the market price for their produce in the nearest town, they text a friend who lives there and ask him to go check out the situation. Why? No infrastructure for 3G let alone  anything with decent internet capability. Motorola made a fortune selling their most basic MOTO brand phones there!

[YNM]

9 minutes ago, softweir said:

Most cell users in Africa use very basic, 2G models.

EDGE can be used for accessing the .net - I have seen this very forum site and even logged in through a Nokia 210 (though the forum's WYSIWYG editor doesn't work on the Opera Mini - boo !), all on EDGE. I have posted from it to phpBB forums.

If we're talking about reach, it is outreached. If we're talking about speed, it is outrun.

Jack of All is King of None. 

[Green Baron]

There is was no infrastructure at all away from the touristic or urban centers and traveling routes (but in the parks actually, funny, a lion with phone ?) when i visited the countries i named above 7 years ago. Many people don't have earnings and live from today to tomorrow, as a white guy hiking alone you better be watchful and don't provoke anything. Leave photo equipment at your place (if it can be locked and isn't just a rigid tent), etc.

I heard there was a program to hand out cellphones free of cost to people, like there was the aid from the state when people bought new cars in western Europe several years ago, but if people can't pay a contract then this makes no sense and i don't know how that went. Maybe (hopefully) things have changed in between, in the course of the global boom we are reportedly living in :-) They certainly have changed here, but still no DSL or cable internet out in the green. 2km farther away, in the village, there is DSL, even ADSL at some places.

 

Ok. But i think we all agree that Starlink must have a broad base of customers to make it pay. And it will be in competition with existing satellites that actually work, so in order to be successful it must be better or cheaper or both. I hope it will be :-)

Edited February 16, 2018 by Green Baron

[CatastrophicFailure]

25 minutes ago, YNM said:

If we're talking about reach, it is outreached. If we're talking about speed, it is outrun.

And yet you’ve had two or three people just right here on this one thread tell you, “hey, this sounds like a good idea, it might just work for me.” 

Starlink doesn’t need to be the end-all be-all to be competitive, in many places simply offering an alternative to the local telco monopoly will get them a few customers, and if it really is “super high speed” even with some latency, that’ll draw a few more. A niche market here, a niche market there... the nice thing about satellites is that they can reach ALL the niche markets at once.

[Green Baron]

2 hours ago, Nibb31 said:

Ships, planes, and remote locations are niche markets, which is why they are not serviced today by the big operators who are in it for the money.

They use Inmarsat as part of the GMDSS. I doubt they'll switch to a different provider if these services are not integrated into that system. I am not sure if Iridium is licensed for the GMDSS too ...

 

Starlink services will probably "just" serve the open public, at least in the beginning.

Edited February 16, 2018 by Green Baron

[KSK]

48 minutes ago, YNM said:

EDGE can be used for accessing the .net - I have seen this very forum site and even logged in through a Nokia 210 (though the forum's WYSIWYG editor doesn't work on the Opera Mini - boo !), all on EDGE. I have posted from it to phpBB forums.

If we're talking about reach, it is outreached. If we're talking about speed, it is outrun.

Jack of All is King of None. 

Perfect is the enemy of good enough.

[YNM]

1 minute ago, KSK said:

Perfect is the enemy of good enough.

Then upgrade.

 

Here's also my thinking : cramming such a pretty powerful device into a 3U cubesat (if it really is cubesat-sized; otherwise it isn't) is a pretty good breakthrough. Why not sell that for replacing the 2G equipment into 3G ? That'd help enticing the upgrade...

Satellites are powered by solar. The same can go for ground-based.

Satellites are also pretty expensive (both the stuff and the launch; yes it could go dozens but I question hundreds as they'll need different orbits). Why not pour that into making the said infra ?

[PB666]

2 minutes ago, Gkirmathal said:

Those points read like it has to discarded a lot of equipment.

My initial though was: an extended upper stage, a.k. larger volume kerlox fuel tanks + ignition fluids, to give it enough D/v and restarts for both:
1) push "a" payload (D2 + D2 lander version) to it's TLI point, and
2) make it back to LEO to be reused for some next mission.

About the fuel transfer problem, the following idea passed through my head (and I know it sounds rather Kerbal-ish).
Mate two upper stages (designed this purpose, pusher and refueler), docked nose to nose, then tumble them to generate a centrifugal force and use electrical pumps to pump fluids from one upper stage tanks the another? Rinse and repeat until the pusher stage it fueled up.

About the D2 stages and their reusability. How to go about making th D2 lander, more reusable? That's a thing I was pondering as well.
Might need an orbiting Lunar station for that.

I am going to realign your logic to fit situations that are more useful.

This shouldn't be a problem once SpaceX converts to Metholox since Liquid Methane creates its own head pressure. I don't think spaceX is going to waste any effort on Falcon beyond GTO.
They could, of course create a 4 booser S1 falcon 9 rocket  (With some S2 redesign) that is capable of sending 25t to Moon intercept, but they have not really expressed any interest in either extending the capability of Falcon beyond FH (due to the recyclability problem of high momentum S1 components), and because their target is Mars. My point is that unless you are sending something on the order of 30t to the moon, its better just to avoid sending men there.

A few of points I would make.

For station keeping in EM stations, Solar/ION is the way to go . . .no need to worry about engine restarts at all. For non-cryotstic fuels you can use an inflatable baffle that can be deflated when not in use and you can use any gas. The problem with Kerolox is the restarting fluid, but for cryofuels there are engines that us electromechanical turbo pumps (very suitable for the low thrusts seen in space) that can prime using fuel rich mixtures of hydrogen and oxygen (spark) in a preignition chamber. Again the problem with Kerosene is its low vapor pressure. This is not a problem at all with methane, ethane, propane, butane.

Alkane           Boiling point  . . . . . . . . . . . . .Triple Point Press
[H₂] . . . . . . . 20 K (−252 °C) . . . . . .12 K . . 0.007 atm  ISP max ~ 500 .Difficult to contain in space
[O₂] . . . . . . . 90 K (−182 °C) . . . . . .54 K . . 0.002 atm  
Methane . .111 K (−161 °C)  . . . . . 90 K . . 0.115 atm      ISP max ~ 400 Can be liquefied under pressure with traditional low temperature refrigerants using two stage cooling.
Ethane . . . 184 K   (−89 °C) . . . . . . 90 K . . near vacuum , Can be liquefied with traditional low temperature refrigerants using two stage cooling.
Propane . . 231K   ( -42 °C) . . . . . . . . . . . . . . . . . . . . . . . . . .Can be liquefied under pressure with typical refridgerants under pressure or low temperature refridgerants.
Butane . . . 273 K  (O C)  . . . . . . . . 134 K  . near vacuum.  Can be liquified with pressure and passive cooling.
Pentane. . . . . . . . 36 'C . . . . . . . . .  . . . . . . . . . . . . . . . . . . . Can simply be liquified with pressure.
Kerosene . . . . . . .65 'C  . . . . . . . . -53'C for aviation fuel.  ISP max ~350

With an improvement in performance in space Kerosene can be made more ignitable with the addition of Butane if the fuel is to be stored above -5'C and propane if the fuel is to be stored above -47'C, or ethane of the fuel is to be stored about -93. Pressure can be governed by having a heater on the fuel tank and using solar panels. You might also want an induction type stirring mechanism in the tank. The risks here is that the fuel should be precooled into Space, provided the craft is reasonably shielded from the sun pressure should be easy to maintain. Propane and Butane are commonly used as fuels for vehicles and houses  . . . .no problem there.



 

[CatastrophicFailure]

19 minutes ago, YNM said:

Then upgrade.

That’s the point you keep missing, bruh. 

Thats not. Always. An option. 

If the telco/cable company doesn’t see economic value in upgrading its equipment, its not going to. To have that economic value there needs to be a certain density of customers in a given area. Many of us live where we do specifically because there isn’t that kind of density, we don’t want it. Satellite internet is already a successful thing in such places, but existing systems have a lot of drawbacks: low bandwidth, per-MB charges, one way High-speed, etc. Also, they’re freaking expensive. 

Starlink has the potential to offer the same kind of coverage, but at prices and performance that will even allow it to compete with telco/cable, perfect for those of us who would be happy with “good enough.” 

[PB666]

28 minutes ago, Green Baron said:

There is was no infrastructure at all away from the touristic or urban centers and traveling routes (but in the parks actually, funny, a lion with phone ?) when i visited the countries i named above 7 years ago. Many people don't have earnings and live from today to tomorrow, as a white guy hiking alone you better be watchful and don't provoke anything. Leave photo equipment at your place (if it can be locked and isn't just a rigid tent), etc.

I heard there was a program to hand out cellphones free of cost to people, like there was the aid from the state when people bought new cars in western Europe several years ago, but if people can't pay a contract then this makes no sense and i don't know how that went. Maybe (hopefully) things have changed in between, in the course of the global boom we are reportedly living in :-) They certainly have changed here, but still no DSL or cable internet out in the green. 2km farther away, in the village, there is DSL, even ADSL at some places.

 

Ok. But i think we all agree that Starlink must have a broad base of customers to make it pay. And it will be in competition with existing satellites that actually work, so in order to be successful it must be better or cheaper or both. I hope it will be :-)

Things have changed, the has been a major push by non-GMOs to aid in the provision of accessibility services to local market places. You can now literally go on line and buy trinkets from some African in a poor village in the middle of nowhere, it might nt reach you soon, but you will eventually get it (otherwise buy on amazon). This is mainly an East Africa thing, the congo and angola are still pretty off the map.

[magnemoe]

7 hours ago, Green Baron said:

Nope. This is a good idea from Musk. Nobody will lay cables to the place where i live for example. The towns have cables, but out in the fields you either have a radio connection to a central antenna (i tried out the provider, they are bad) or satellite. Satellite is ok, but if it had competition they'd do much better.

Problem: Satellite is in GSO. Which means 0.2 seconds for up and down communication. A dynamically built page that asks many ad servers, google, facebook, youtube and all those so-called social things takes time. I mean TIME, like 20-30 seconds or more. I can block outgoing calls to those annoying services from my network, but that only counts for a half. Downloads of continuous data like updates etc. otoh are relatively fast (the contracted speed actually).

So, if spacex would actually provide that service for reasonable conditions (like less than 30funds/month, >3Mbit/s, more than 30GB/month or better unlimited) i'd be a customer.

This, I guess more than 10% of population in the US will benefit from this. more in many other countries.  
Some mentioned planes and ships, I will add cars who will become more relevant over time 

Note that satellite broadband work pretty opposite of cable, cable is easier with higher population density, satellite have an fairly fixed bandwidth for its area so with fewer users each get more bandwidth. 
Another bonus is that it bypasses censorship very smoothly. Net neutrality can be another major factor as it bypasses the traditional major isp, 
And as an bonus since the satelites are pretty cheap and mass produced they can use old at end of usable life rockets to launch them on. 

[YNM]

28 minutes ago, CatastrophicFailure said:

Thats not. Always. An option.

But it eventually will be. Which means market grab.

30 minutes ago, CatastrophicFailure said:

To have that economic value there needs to be a certain density of customers in a given area.

... Orr get a much cheaper device with similar capabilities. The 12,000 3U cubesats clearly possess this, othewise they themself won't work.

13 minutes ago, magnemoe said:

Another bonus is that it bypasses censorship very smoothly.

Why would a service offered by one company somehow escapes their own "censorship" ? If it's so bad, get a VPN. Or Tor.

 

Telco companies are very often close to national carriers. They have the obligation to improve their own image (tell me a country that tries to deface itself). In all seriousness, if communications are considered public need, the gov't can always do something about it.

 

But yeah, maybe it'll work for the Pacific islands. If they're interested in .net that is !

[Green Baron]

47 minutes ago, CatastrophicFailure said:

[snip], we don’t want it. [snip]

:-)

[tater]

LOL.

https://arxiv.org/pdf/1802.04718.pdf

 

[Green Baron]

13 minutes ago, YNM said:

... Orr get a much cheaper device with similar capabilities. The 12,000 3U cubesats clearly possess this, othewise they themself won't work.

A single (big) satellite can cover half a continent with 100 TV programs and high speed internet for millions. Only problem: it is in GSO, aka far away. One needs a dish in the garden. But they have immense capabilities to buffer content, think pages in advance, etc. It is just, dynamically built pages, like news pages, pub science, etc. take time.

A lower flying swarm might actually improve link times, but buffering and broader services are not their thing, too small. At least i can't imagine how ... we must wait & see :-)

[Green Baron]

13 minutes ago, tater said:

LOL.

https://arxiv.org/pdf/1802.04718.pdf

 

"chaotic orbit", "predictions impossible" ....

... similarities with actual SpaceX timelines are of course incidental ?

Edit: Hey, i'm trying to be funny. They did a really good job with the launch i think !

Edited February 16, 2018 by Green Baron

[justidutch]

49 minutes ago, magnemoe said:

Some mentioned planes and ships, I will add cars who will become more relevant over time 

…and watches.  And glasses, and neural implants, and bicycles, and skateboards, jetpacks, and anything else we can imagine to be quite-near-future that could in some way use an internet connection.