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« Last post by Paul451 on Today at 10:30 AM »
If "moon" is just a subclass of all substellar objects in the solar system, then so are "planets", by any definition. And no more or less valid than any other subclass, such as SDO or KBO or main-belt object. llanitedave was trying to suggest that we never classify things after their location or extrinsic properties, when it's actually very common in the solar system. And "moon" is the perfect example. A whole classification based solely on a single extrinsic property, a substellar object in the solar system being in orbit around some other substellar object, regardless of whether that "some other" is Jupiter or a small asteroid. And in bold is not what illanitedave is suggesting.
I can think of no other scientific definition of any class of objects where intrinsic characteristics of the objects themselves are completely absent.
How does "moon" not meet llanitedave's requirement of a classification based purely on extrinsic/location/environmental properties?
"Moons" are implicitly a sub-category of the broader class of all substellar objects, but explicitly so are IAU-Planets. Both are dynamical subcategories of the broader intrinsic class (substellar masses).
Just as KBOs are a dynamical sub-category of the broader class of substellar non-planetary objects.
We are suggesting that [...] at the top of the sub-stellar taxonomy "planet" should be the set of sub-stellar bodies that are round no matter their dynamical circumstances ... or composition.
IMO, extrinsic classification of even sub-planetary objects is more scientifically useful. KBO, SDO, main-belt asteroid, Trojan, etc.
What is the point in placing an arbitrary intrinsic property first? You separate objects of extrinsic similarity
. For what reason? What is the benefit of grouping Ceres with Pluto, Pluto with Eris, instead of grouping them first
with their neighbours and siblings. What scientific usefulness is served by such a grouping? What science has been harmed by the previous lack of such "roundness" classification?
« Last post by jpo234 on Today at 10:22 AM »
1. Space is hard. Space will always be hard.
Once the technology is settled, it shouldn't be hard. I suspect that people initially thought the same about every new technological frontier. Once good solutions and practices are established, things become routine.
Airplanes are still highly complex systems, but once you have built thousands of them, it's just routine.
« Last post by Paul451 on Today at 10:22 AM »
I'm talking about the lower mass boundary for the geophysical planet definition.
As with any continuous sequence (mass in this case) as you approach the boundary (mass necessary to be spherical) you run into borderline examples.My point was that there aren't boundaries in a continuous sequence.
There is no "mass boundary". Any intrinsic property depends not just on mass, but on the composition, age, closeness to the sun of the object, and varies wildly between objects of the same mass.
You can draw arbitrary lines on a continuum, just for the sake of nomenclature, if no other arrangement presents itself. But if the universe presents you with an existing wide separation of classes of objects, why reject it? Why choose a greatly inferior classification system?
The lowest mass "round" body in the Solar System is Mimas and its mass serves well enough as the lower mass limit for "planet"
Serves what? What scientific need is served by it?
Instead of a distracting focus on why Pluto is no longer a planet, the focus for kids could have been an awe factor as to how many new planets there are.
"Oh, somebody please think of the children!"
The focus of instruction becomes understanding the structure and types of bodies within the Solar System:
1. What is significant about planets being round?
2. What types of orbits do planets have? Dynamically dominant (Principal planets), dynamically not dominant (Belt planets), planets that orbit a bigger planet (moons), planets that don't orbit any star (rogue).
And the concerns of the dynamical perspective are addressed - not ignored. In fact, calling the IAU planets "Principal planets" would make pretty big impression on students in school - "You know how the Principal is the person in charge of the school? Well, the Principal planets - like the Earth and Jupiter - are the big planets that dominate the orbits in the Solar System."
The people who fussed over the "demotion" of Pluto are not the sort of people who would have explained dynamical dominance, or hydrostatic equilibrium, or anything else. Those who didn't understand the concepts made no attempt to understand the IAU definition, and those who did understand it, not only made no attempt to explain the science behind it, but went out of their way to encourage public misunderstanding.
Your "won't somebody think of the children" plea assumes the people who opposed the IAU definition are acting honestly and with the broader interests of science at heart. But I see nothing to suggest that.
« Last post by Rei on Today at 09:26 AM »
Lets not forget that with a Mars colony as planned there will be a bunch of full size ITS boosters sitting idle between synods unless they have a job.
The bigger issue is what to do with the spaceships between synods, since according to SpaceX's figures, they're the most expensive part of the system - yet would just be sitting idle most of the time.
*Cough* Venus *cough*. Sorry, clearing my throat.
« Last post by Rei on Today at 09:22 AM »
My two cents: F9 will be around until composite cryogenic stages are reliable. And then it will be gone in about five years. Regardless of anything concerning ITS.
* Switching to methane won't give enough of a performance benefit to justify throw away all of their progress toward turning F9 into a workhorse.
* F9 and F9H justify the overwhelming majority of payloads; if SpaceX wants something bigger than that, they're going to push toward ITS
* On the other hand, the big strength to weight advantage of advanced composites over aluminum could well justify a new rocket. But composites + cryogens (particularly LOX) is anything but easy.
If they can mature composite cryogen tanks, and get the budget / justification for a very large rocket, they'll make ITS - or without the budget for ITS, something smaller, ultimately replacing either F9, FH, or both. But until then, I can't see financial justification for them to switch from LOX / RP-1 in aluminum. Lots of capital cost, lots of time, minimal return on investment.
So, I finally read through this book to the end. (yes, I'm a speed-reader and no, I don't have a 9-to-5 job). I have the two earlier editions and some of the less relevant material in them has been omitted to fit within the 3-volume limit.
But there is a vast amount of additional material, not just about the later missions but much about the historical background. Did you know that:
- the X-20/Dyna-Soar pilot would have been issued an AR-15 rifle for disabling Soviet satellites
- many eminent experts such as Bob Truax and Wernher von Braun were secret shuttle skeptics
- Klaus Heiss of the infamous "Mathematica Study" was so confident in the results that he formed a company to build an extra Orbiter with private capital and lease it to NASA
- the management at Rocketdyne became convinced that the staged-combustion cycle of the SSME was unworkable and tried to get Marshall to switch to a gas-generator design with lower pressures (similar to those in the final Block II SSME)
(Historical nitpick: Jenkins repeats the standard fiction spread by the promoters of the doomed X-38 project that PRIME/X-23A and X-24A had the same configuration and proved its stability at all Mach numbers -- the photos in the book show that the two vehicles were very different.)
For a guy who worked on the program most of his professional life, Jenkins is surprisingly objective about the Shuttle's design weaknesses and the engineering and management failures that led to the two losses and several groundings. He uses some very harsh words about the promised flight rates and reveals internal studies that showed these to be nonsense. Since this isn't a political history he doesn't explore why NASA HQ continued to promise 24 flights per year up to 1986.
Of course the roles of USAF, NRO, and NSA in Shuttle are still concealed by secrecy but there is a good sense of why the space intelligence community first embraced and then rejected shuttle.
Much of volume 3 is devoted to summaries of each mission. Even the most obscure flights of Shuttle's boring middle years get at least 2 pages. The major accidents and groundings have comprehensive coverage. All the proposed upgrades are discussed along with the confusing succession of Shuttle-C and Shuttle-Z proposals. There is a whole chapter devoted to the Vandenburg SLC-6 fiasco. Upper stages and the lack of same get a good treatment, except there is still no technical reason given for the cancellation of Centaur-G and Centaur-G'.
Finally there is a comprehensive discussion of the dismemberment of the surviving Orbiters for the Constellation program, and the installation of fake components for museum display (something future generations will surely regret).
A section on costs shows that each Shuttle mission cost exactly $1.642B in FY2012 dollars, not counting NASA Center support and civil service salaries. Allowing 25-30% extra for these costs brings the per-mission cost up over $2B.
Since this launch will probably represent the start of a totally new chapter in spaceflight, or at least we hope, here are twenty things off the top of my head that have been learned through blood sweat and tears up to this point:
1. Space is hard. Space will always be hard.
2. Building rockets is hard at first but gets semi-easier as a knowledge and data bases are developed. Also advancments in computer power and modeling help greatly.
3. Flight rationale is derived from how hard you test but far more by how much components fly.
4. Keep it simple stupid. The more complex a system is the more things can go wrong.
5. Building really big rockets eventually becomes easy, but making them economically viable is imuch harder (especially if you throw them away after use).
6. Throwing away complex and expensive vehicles after only one or a handful of uses doesn't work.
7. Government only spaceflight is a starting point but is not viable in the long term. Pushing the envelope for the sake of technology or pork does not work either (venture star, cxp and many more).
8. Government should provide the means and support to lead but cannot be the source of exploration.
9. Space must be made economically viable to access otherwise it will never be developed or accessed.
10. There are very compelling if not totally demanding reasons to explore and develop our solar system.
11. Winged lifting body vehicles or any vehicle requiring a complex heat shield that wastes much of its mass on the vehicle itself are not the way to go. They work (for leo) but require massive overhaul and bring extra complexity and risk, at least given current technology.
12. Wasted upmass is wasted money.
13. Rockets are not legos.
14. Politicians should not build rockets.
15. The commercial industry actually can do it (sometimes harder to believe than to see).
16. Re-usability is the key to the future of exploration if there is one to be had.
17. Human spaceflight is very very hard but it can be gradually made easier.
18. Space stations are very good ideas but building them in small pieces may or may not have been, the jury is still out.
19. We have alot more to learn.
20. Never give up.
Here's to everything so far, and yes this leaves alot out feel free to debate it. Really hope this thing works, if it does the theory is no longer theory. What comes next is how to make it more easily reproduce-able and capitalize on it, but the hardest part is the first shot. I really hope it works.
« Last post by calapine on Today at 09:02 AM »
Evolution of Arianespace governance ensures greater coherence with Airbus Safran Launchershttp://www.arianespace.com/press-release/evolution-of-arianespace-governance-ensures-greater-coherence-with-airbus-safran-launchers/Summary:
Arianespace shareholders voted unanimously to convert the launch operator and subsidiary of Airbus Safran Launchers to an SAS (simplified joint-stock company) at the company’s Annual General Meeting, held in Paris on Monday, March 27.
The modification aims to streamline and modernize Arianespace’s governance to achieve greater responsiveness, facilitate relationships with industrial prime contractors, and be coherent with the new shareholder structure of Arianespace Participation.
The new legal form also comes with changes to the governance of Arianespace, allowing for more cohesive working coordination between the launch operator and its parent company, the Ariane launcher prime contractor. With these changes, Airbus Safran Launchers CEO, Alain Charmeau, also becomes Chairman of the Board of Directors of the holding company, Arianespace Participation. Stéphane Israël, CEO of Arianespace SAS, and CEO of Arianespace Participation, joins the Executive committee of Airbus Safran Launchers as Director of Ariane 5 and Ariane 6 commercial launcher programs. This position had been held provisionally by Alain Charmeau.
“This evolution in governance is consistent with the steps taken since 2014 to streamline the European launcher industry. It places the entire industrial organization of Ariane 5, from production to marketing, under the sole responsibility of Stéphane Israël, while preparing for the optimal development, production and commercialization of Ariane 6 for the benefit of Arianespace’s customers”, said Alain Charmeau.
Stéphane Israël added: “With this new governance, Arianespace will be able to rely on its industrial prime contractor and biggest shareholder, Airbus Safran Launchers, to be even more responsive to customer needs and market developments. I would like to thank Alain Charmeau for his trust. The synergies I will strive to create between Arianespace and Airbus Safran Launchers will bring opportunities for all their teams. In this new configuration, Arianespace will further integrate operations with Avio/ELV for the success of Vega and confirms its commitment to Soyuz operations with its partner Roscosmos.”
This change was submitted to ESA on 16 March after being approved by Arianespace staff representatives in February 2017. Airbus Safran Launchers has held a 74% stake in Arianespace since 31 December 2016.
- Arianespace becomes an 'Société par actions simplifiée' (similar to the American LLC)
- Stephane Isreal joins the Airbus Safran Lauchers board as 'Director of commercial launcher programs'
« Last post by Bynaus on Today at 09:02 AM »
Falcon 9 will simply be around until something better comes along. Better as in lower long-term cost per kg delivered to space, as this is the one metric which determines how good SpaceX is doing its main job and how it holds up against competitors.
As the long-term costs for the F9 system are not yet known (e.g., how many times can a core actually be re-used, what is the refurbishment going to cost on average and as a function of past reuses, what price reductions are the customers and insurance companies expecting for reflights, etc), it is impossible to say right now for how long the system will last. It is way too early to speculate if and when F9/FH will be replaced by ITS, in particular since the former is an actual operational rocket in advanced stages of development whereas the other is still (mostly) a paper rocket.
I think it is possible, but by no means certain, that there will be a "Falcon 9 NG" (NG for next generation or, also, natural gas
) vehicle which will incorporate all the lessons learned with the F9 and further improve re-usability (including the upper stage), but it may be just as likely that the F9/FH family will eventually be replaced completely by a system based on the ITS booster. Again, this depends on how the market develops and reacts to the increased capabilities and reduced prices.
So, nothing is set in stone, and the situation will have to be assessed over and over again. Anything Elon says about the future of the F9/FH is based on his current reading of the situation, but I have no doubt that he would change his mind quickly if needed.
« Last post by vanoord on Today at 08:19 AM »
Looking at the update sheet it looks like someone decided they needed to put information about the launch vehicle to fill the space. Should it be taken as 100% fact?
Presumably the choice of S1 booster is made some time out but *could be* subject to change if the order of flights changes.
There are potentially two new cores due to be flown before CRS-11 (NROL-76 and Inmarsat-5 F4), but if there are slips with launches and a need to get CRS-11 aloft, there would be an option for CRS-11 to be brought forward and use the booster that's currently pencilled in for Inmarsat-5?
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