Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 34
  1. #21
    RGClark's Avatar
    RGClark is offline White Dwarf
    Points: 7,442, Level: 60
    Level completed: 46%, Points required for next Level: 108
    Overall activity: 0%
    Join Date
    Jul 2009
    Location
    Philadelphia, USA
    Posts
    43
    Points
    7,442
    Level
    60
    Thanks
    1
    Thanked 8x 7 Posts

    Default



    Just saw this:


    The SpaceX Falcon Heavy Booster: Why Is It Important?
    by John K. Strickland, Jr.
    September, 2011
    What amazes people is that SpaceX has broken the long-sought 1,000
    dollars a pound to orbit price barrier with a rocket which is still
    expendable. "How can he (SpaceX CEO Elon Musk) possibly do this?" they
    ask. The Chinese have said flatly that there is no way they can
    compete with such a low price. It is important to remember that this
    was not done in a single step. The Falcon 9 already has a large price
    advantage over other boosters, even though it does not have the
    payload capacity of some of the largest ones. The 'Heavy' will even
    this score and then some. At last count, SpaceX had a launch manifest
    of over 40 payloads, far exceeding any current government contracts,
    with more being added every month. These are divided between the
    Falcon 9 and the Falcon Heavy.
    I think the most important accomplishment of SpaceX might turn out
    to be that they showed in stark terms that privately financed spacecraft,
    both launchers and crew capsules, can be accomplished at 1/10th the
    developmental cost of government financed ones. Imagine a manned,
    reusable orbital launcher, for example, instead of costing, say, $3 billion,
    only costing $300 million to develop.
    As I argue, the key variable that made this reduction possible is that
    the launcher was privately financed. That is, it was the launch
    company's own money that was financing its development. In that case
    it makes sense the company would be more fiscally responsible in
    developing it.
    Then the first step in reducing the price to orbit is making the
    vehicles be privately financed. But if the launch companies are going
    to spend their own money, they have to be convinced they can make a
    profit on them. This will come if there is a significant market.
    My view is that there would be a significant market for small,
    privately owned, SSTO's. When you consider that with orbital refueling
    such craft can also make lunar missions, the market becomes even more
    apparent.
    An additional finance stream of such vehicles that would make them
    marketable I argue could be salvage of satellites in LEO or GEO:

    Space junk at 'tipping point', now getting worse on its own ? The Register
    More collisions generate more debris, so more collisions.
    By Gavin Clarke
    Posted in Space, 2nd September 2011 11:18 GMT


    Article:
    World's First Space Gas Station for Satellites to Launch in 2015 | Space Junk, Orbital Debrs & In-Space Satellite Refueling | Satellite Servicing and Refueling, SIS Satellite | Space.com
    by Clara Moskowitz, SPACE.com Senior Writer
    Date: 15 March 2011 Time: 06:03 PM ET
    Until now, satellites orbiting around Earth have been limited by how
    much fuel they carry onboard. Once those tanks run dry, the satellites
    die, sometimes languishing in space as uncontrollable debris that then
    poses the risk of colliding with other spacecraft.
    The new plan offers the potential not just to extend the lives of
    working satellites, but to help combat the growing space junk problem.
    The satellite, called the Space Infrastructure Servicing (SIS)
    vehicle, is designed not just to transfer more fuel into existing
    satellites, but to inspect, tow, reposition and make minor repairs to
    them.
    In addition to its tank of fuel, the refueling satellite will carry a
    robotic arm that can be used to grab onto satellites and tug at stuck
    solar array panels, for example, or attempt other minor fixes to
    broken parts.
    "This is a first-time-ever, huge, huge, huge event," said Andrew
    Palowitch, director of the Space Protection Program, a joint project
    of U.S. Air Force Space Command and the National Reconnaissance
    Office, speaking at a National Research Council workshop on orbital
    debrislast week.
    Palowitch stressed that the ability to tow or refuel dead satellites
    in order to steer them out of the way would have a big impact on the
    growing problem of dangerous space debris clogging the crowded
    corridors of Earth orbit. [Worst Space Debris Events of All Time]
    "In the context of debris removal, this is the absolute best and
    absolute most fantastic new venture for the entire space community,"
    he said.
    The refueling satellite will be able to move dead spacecraft to
    what's called the "graveyard orbit," where they are high enough that
    they should not pose a risk to working satellites, or maneuver them
    low enough that they break apart in Earth's atmosphere.

    Remember the TV show Salvage 1?



    Bob Clark

  2. #22
    RGClark's Avatar
    RGClark is offline White Dwarf
    Points: 7,442, Level: 60
    Level completed: 46%, Points required for next Level: 108
    Overall activity: 0%
    Join Date
    Jul 2009
    Location
    Philadelphia, USA
    Posts
    43
    Points
    7,442
    Level
    60
    Thanks
    1
    Thanked 8x 7 Posts

    Default

    Just saw this article on The Space Review discussing a recently discovered copy of a 1963 TV interview with Arthur C. Clarke:

    The perils of spaceflight prediction.
    by Jeff Foust
    Monday, December 5, 2011
    The Space Review: The perils of spaceflight prediction

    In the interview Clarke gives some predictions of the future of space exploration. From the standpoint of the beginnings of human spaceflight, he suggests a manned Mars mission within 25 years, which would have been by 1988, and Moon bases by the end of the 20th century.
    This turned out to be too optimistic. But as I argued above, this could indeed have been technically and even financially feasible: if it had been recognized that reusable SSTO's are possible, and in fact aren't even really hard, then we would have had routine, private spaceflight by the 1970s.
    Such wide spread, frequent launches using reusable spacecraft would have cut the costs to space by two orders of magnitude, at least. This would then have made the costs of lunar bases and manned Mars missions well within the affordability range.
    The important point is that the required high efficiency engines and lightweight stages for SSTO's already exist and have for decades. All that is required is to marry the two together. An expendable test SSTO could be produced, like, tomorrow. Just this one simple, cheap test would finally make clear the fact that routine spaceflight is already doable.


    Bob Clark
    If you use both the most weight efficient structures and the best sea level-to-vacuum efficient engines at the same time,
    then what you will wind up with will be a SSTO whether you intend it to or not.
    Blog: http://exoscientist.blogspot.com

  3. #23
    Modlerbob's Avatar
    Modlerbob is offline Bright Giants
    Points: 3,373, Level: 38
    Level completed: 16%, Points required for next Level: 127
    Overall activity: 0%
    Achievements:
    365 Days+ Registered Achievement!50 Posts Achievement!5 Threads Achievement!First 1000 Experience Points200+ Posts Achievement!
    Join Date
    Apr 2011
    Location
    DeBary, Fl.
    Posts
    244
    Points
    3,373
    Level
    38
    Thanks
    15
    Thanked 36x 32 Posts

    Default

    Unfortunately the leaders of the world chose to waste our resources on stupid things like warfare instead of great things like exploring space.
    Bob DeWoody

  4. #24
    RGClark's Avatar
    RGClark is offline White Dwarf
    Points: 7,442, Level: 60
    Level completed: 46%, Points required for next Level: 108
    Overall activity: 0%
    Join Date
    Jul 2009
    Location
    Philadelphia, USA
    Posts
    43
    Points
    7,442
    Level
    60
    Thanks
    1
    Thanked 8x 7 Posts

    Default

    Elon Musk has said he wants to cut the costs to space to the $100 to $200 per kg range by reusability. This is about a two order of magnitude reduction in cost. To put this in perspective, this is like a trans-atlantic flight that costs $1,000 suddenly being cut to cost $10 to $20.
    Musk has said this transformation of the Falcon 9 to full reusability will be very hard. I don't believe it will be. But first, keep in mind how important that reduction in cost will be if it succeeds. If it succeeds then SpaceX will monopolize the launch business if the other launch companies do not field their own reusable vehicles. So there is a tremendous financial incentive for SpaceX to invest in reusability. Now, most in the industry believe reusability is very difficult for orbital vehicles and not even worth the expense. So if Musk reinforces that idea then he has a better chance at being able to field one without the other launch providers having one. And since they will not have even started to develop one, it will take them some time to catch up. The effect is that Musk will have a monopoly on all launches for at least a few years.
    I don't know if that is Musk's intent in saying reusability is very hard. Actually I'm inclined to believe he is just saying what most in the industry believe including his own engineers. But a key reason why reusability is not very hard is because the cost in mass in reentry and landing systems is surprisingly low. In regards to the technical difficulty, there is none. We know how to do it as the shuttle orbiter and the X-37B and Dragon spacecraft has shown. I include the Dragon in the list of reusables because its heat shield showed minimal degradation on return. Musk has said the same heat shield could make hundreds of flights, at least to LEO.
    I made an estimate before of about 28% of the landed mass has to go to reentry/landing systems. This was based on estimates of 15% for thermal protection, 10% for wings or for propellant for vertical landing, and 3% for landing gear. However, I said likely with modern materials this could be cut to half that. In fact, it might even be lower than 10%.

    1.)Weight of thermal protection.

    Robert Zubrin has given an estimate of 15% of the landed weight for the weight of thermal protection systems(TPS):

    Reusable launch system.
    Reusable launch system - Wikipedia, the free encyclopedia

    However, I gather this was in relation to the older capsules, Mercury, Gemini, Apollo, etc. Indeed the weight of the ablative heat shield on the Apollo capsule was about 15%:

    Apollo Command/Service Module.
    2.7 Specifications
    Apollo Command/Service Module - Wikipedia, the free encyclopedia

    However, the space shuttle with its mostly silica tiles was able to reduce the TPS weight to about 8% of the maximum landing weight of 104,000 kg:

    Space Shuttle thermal protection system.
    3.3 Weight considerations.
    Space Shuttle thermal protection system - Wikipedia, the free encyclopedia

    Also, for the X-37B the TUFROC leading edge material instead of the shuttles RCC and the TUFI AETB material instead of the shuttles silica tiles are either of equal or lower weight than the shuttles TPS materials while being tougher and requiring less maintenance:

    X-37B Orbital Test Vehicle.
    Boeing: X-37B Orbital Test Vehicle

    For ablative TPS, the PICA-X material used on the Dragon capsule weights about half the weight of the AVCOAT material used on the Apollo heat shield:

    Re: Dragon v/s Orion.
    Dragon v/s Orion

    while being able to still survive lunar and even Martian reentry speeds.

    SpaceX has found that at least for LEO reentry speed judging from the minimal degradation on the Falcon 9/Dragon test flight, the PICA-X heat shield could be reused hundreds of times.

    Also, for vertical powered landings a la the DC-X, you might not even need an extra heat shield for base first landings. One proposal for a VTVL SSTO uses low thrust during the descent as well as a high temperature-resistant aerospike nozzle to serve as the reentry thermal protection. You would need to retain more mass in propellant or some inert gas for this purpose though.
    Another idea for a vertical landing vehicle would be to reenter head first. This was the preferred method of the Air Force since it provided increased cross-range. In that case you would have the blunt heat shield at the top of each stage. I thought this method would be unstable with the heavy engines now at the top during reentry, but since this was considered for the orbital version of the DC-X presumably this was solved.

    2.)Weight of the wings and the landing gear.

    For horizontal landing, a common estimate is that the weight of wings is 10% of the landed weight. This comes from aircraft examples though where the wings have to carry the weight of the fuel which can be as much as the dry weight of the aircraft itself or more.
    An example where the propellant will not be carried in the wings and lightweight composites will be used is the Skylon. According to their released specifications the wing weight will be less than 2% of the take-off weight, which is the appropriate weight to compare to for a horizontal take-off vehicle:

    The SKYLON Spaceplane.
    by Richard Varvill and Alan Bond
    Journal of the British Interplanetary Society, Vol. 57. pp. 22–32, 2004
    p. 32.
    http://www.reactionengines.co.uk/dow..._v57_22-32.pdf

    On that same page the landing gear weight is the only 1.5% of the take-off weight.
    Then for a vertical take-off vehicle these low weight proportions should apply to the dry, landing weight.


    Bob Clark
    If you use both the most weight efficient structures and the best sea level-to-vacuum efficient engines at the same time,
    then what you will wind up with will be a SSTO whether you intend it to or not.
    Blog: http://exoscientist.blogspot.com

  5. #25
    Lj3d's Avatar
    Lj3d is offline Bright Giants
    Points: 1,342, Level: 21
    Level completed: 43%, Points required for next Level: 58
    Overall activity: 0%
    Achievements:
    50 Posts Achievement!Ghost Achievement! Averaging 5+ posts a day!200+ Posts Achievement!5 Threads Achievement!400+ Posts Achievement
    Join Date
    Jan 2012
    Location
    United States
    Posts
    245
    Points
    1,342
    Level
    21
    Thanks
    12
    Thanked 26x 21 Posts

    Default

    The Delta Clipper (DC-X) was a prototype vehicle designed to test the SSTO concept. It stood about 43' tall. Plans were drawn up in 1993 for construction of the DC-Y, a 127' tall full SSTO vehicle to be tested in 1999 IIRC. But by 1996 the Venture Star was selected for full scale development.

  6. #26
    Tim K's Avatar
    Tim K is offline Bright Giants
    Points: 8,315, Level: 63
    Level completed: 55%, Points required for next Level: 135
    Overall activity: 0%
    Achievements:
    365 Days+ Registered Achievement!750 Days+ Registered Achievement!First 1000 Experience Points1000 Days+ Registered Achievement!3 Years + Achievement
    Join Date
    Dec 2008
    Location
    Colorado
    Posts
    249
    Points
    8,315
    Level
    63
    Thanks
    45
    Thanked 93x 70 Posts

    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    The problem with any SSTO using chemical engines is the poor mass ratio. This is not amenable to breakthroughs or clever design, it's enforced by the math of the rocket equation. With chemical rocket engines we can't get more than one or two percent of the initial mass of a single-stage vehicle into orbit. The other 98% is fuel burned to get there. A 20-ton SSTO on orbit would have a liftoff weight of 1000 tons!

    Nuclear engines make SSTO possible/practical, and the liftoff weight of that same vehicle could be reduced to 100-200 tons. What are the chances of that happening?

  7. #27
    Modlerbob's Avatar
    Modlerbob is offline Bright Giants
    Points: 3,373, Level: 38
    Level completed: 16%, Points required for next Level: 127
    Overall activity: 0%
    Achievements:
    365 Days+ Registered Achievement!50 Posts Achievement!5 Threads Achievement!First 1000 Experience Points200+ Posts Achievement!
    Join Date
    Apr 2011
    Location
    DeBary, Fl.
    Posts
    244
    Points
    3,373
    Level
    38
    Thanks
    15
    Thanked 36x 32 Posts

    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    Quote Originally Posted by Tim K View Post
    The problem with any SSTO using chemical engines is the poor mass ratio. This is not amenable to breakthroughs or clever design, it's enforced by the math of the rocket equation. With chemical rocket engines we can't get more than one or two percent of the initial mass of a single-stage vehicle into orbit. The other 98% is fuel burned to get there. A 20-ton SSTO on orbit would have a liftoff weight of 1000 tons!

    Nuclear engines make SSTO possible/practical, and the liftoff weight of that same vehicle could be reduced to 100-200 tons. What are the chances of that happening?
    Heck, the anti nukers got all bent out of shape when all they launched was a nuclear power cell for the Cassini probe. They would probably over run Cape Canaveral if word that a nuclear powered rocket was being prepped for launch.
    Bob DeWoody

  8. #28
    Tim K's Avatar
    Tim K is offline Bright Giants
    Points: 8,315, Level: 63
    Level completed: 55%, Points required for next Level: 135
    Overall activity: 0%
    Achievements:
    365 Days+ Registered Achievement!750 Days+ Registered Achievement!First 1000 Experience Points1000 Days+ Registered Achievement!3 Years + Achievement
    Join Date
    Dec 2008
    Location
    Colorado
    Posts
    249
    Points
    8,315
    Level
    63
    Thanks
    45
    Thanked 93x 70 Posts

    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    Quote Originally Posted by Modlerbob View Post
    Heck, the anti nukers got all bent out of shape when all they launched was a nuclear power cell for the Cassini probe. They would probably over run Cape Canaveral if word that a nuclear powered rocket was being prepped for launch.
    Back in the '90s DARPA had a project that developed a pebble-bed nuclear rocket engine. The engine was made of pea-sized carbide balls with a tiny core of nuclear fuel in the center of each ball. These balls were loosely packed in a "combustion" chamber with a fuel inlet on one side and a rocket nozzle on the other. No moving parts, and no large chunks of radioactive metals. Fuel entering the chamber acted as the moderator to start the nuclear reaction and heating, and when the fuel ran out, the reaction stopped. In the event of a catastrophic failure, the balls could get dispersed, but they are small and rugged enough that it is likely they would remain intact.

    This project actually got to the point where a test launch was planned from Kwajalein Island -- then the politicians found out about it.

  9. #29
    RGClark's Avatar
    RGClark is offline White Dwarf
    Points: 7,442, Level: 60
    Level completed: 46%, Points required for next Level: 108
    Overall activity: 0%
    Join Date
    Jul 2009
    Location
    Philadelphia, USA
    Posts
    43
    Points
    7,442
    Level
    60
    Thanks
    1
    Thanked 8x 7 Posts

    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    Quote Originally Posted by Tim K View Post
    The problem with any SSTO using chemical engines is the poor mass ratio. This is not amenable to breakthroughs or clever design, it's enforced by the math of the rocket equation. With chemical rocket engines we can't get more than one or two percent of the initial mass of a single-stage vehicle into orbit. The other 98% is fuel burned to get there. A 20-ton SSTO on orbit would have a liftoff weight of 1000 tons!

    Nuclear engines make SSTO possible/practical, and the liftoff weight of that same vehicle could be reduced to 100-200 tons. What are the chances of that happening?
    Actually, we did have a launch system that bad, the space shuttle system. It was actually even worse; the payload fraction was about 1%.
    But see this page for examples of proposed SSTO's with payload fractions in the 3% range, comparable to many expendable rockets:

    Space Future - A Single-Stage-to-Orbit Thought Experiment
    Gary C Hudson

    Bob Clark
    If you use both the most weight efficient structures and the best sea level-to-vacuum efficient engines at the same time,
    then what you will wind up with will be a SSTO whether you intend it to or not.
    Blog: http://exoscientist.blogspot.com

  10. The Following User Says Thank You to RGClark For This Useful Post:

    Tim K (07-22-2012)

  11. #30
    RGClark's Avatar
    RGClark is offline White Dwarf
    Points: 7,442, Level: 60
    Level completed: 46%, Points required for next Level: 108
    Overall activity: 0%
    Join Date
    Jul 2009
    Location
    Philadelphia, USA
    Posts
    43
    Points
    7,442
    Level
    60
    Thanks
    1
    Thanked 8x 7 Posts

    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    No, SSTO is not a four-letter word, though it is sometimes treated that way by those in the industry.
    I've been arguing that SSTO's are actually easy because how to achieve them is perfectly obvious: use the most weight optimized stages and most Isp efficient engines at the same time, i.e., optimize both components of the rocket equation. But I've recently found it's even easier than that! It turns out you don't even need the engines to be of particularly high efficiency.
    SpaceX is moving rapidly towards testing its Grasshopper scaled-down version of a reusable VTVL Falcon 9 first stage:

    Reusable rocket prototype almost ready for first liftoff.
    BY STEPHEN CLARK
    SPACEFLIGHT NOW
    Posted: July 9, 2012
    Spaceflight Now | Breaking News | Reusable rocket prototype almost ready for first liftoff

    SpaceX will be duplicating in this what the DC-X accomplished in the early 90's. The DC-X was a scaled down, low altitude test vehicle for a full-scale SSTO VTVL vehicle. So could the full-sized Falcon 9 first stage act as a VTVL SSTO?
    SpaceX deserves kudos for achieving a highly weight optimized Falcon 9 first stage at a 20 to 1 mass ratio. However, the Merlin 1C engine has an Isp no better than the engines we had in the early sixties at 304 s, and the Merlin 1D is only slightly better on the Isp scale at 310 s. This is well below the highest efficiency kerosene engines (Russian) we have now whose Isp's are in the 330's. So I thought that closed the door on the Falcon 9 first stage being SSTO.
    However, I was surprised when I did the calculation that because of the Merlin 1D's lower weight the Falcon 9 first stage could indeed be SSTO. I'll use the Falcon 9 specifications estimated by GW Johnson, a former rocket engineer, now math professor:

    WEDNESDAY, DECEMBER 14, 2011
    Reusability in Launch Rockets.
    An Ex Rocket Man's Take On It: Reusability in Launch Rockets

    The first stage propellant load is given as 553,000 lbs, 250,000 kg, and the dry weight as 30,000 lbs, 13,600 kg. The Merlin 1C mass hasn't been released, but I'll estimate it as 650 kg, from its reported thrust and thrust/weight ratio. The Merlin 1D mass has been estimated to be 450 kg. Then on replacing the 1C with the 1D we save 9*200 = 1,800kg from the dry weight to bring it to 11,800 kg.
    The required delta v to orbit is frequently estimated as 30,000 feet per second for kerosene-fueled vehicles, 9,144 m/s. When calculating the delta v your rocket can achieve, you can just use your engines vacuum Isp since the loss of Isp at sea level is taken into account in the 30,000 fps number. Then this version of the Falcon 9 first stage could lift 1,200 kg to orbit:

    310*9.81ln(1 + 250/(11.8 + 1.2)) = 9,145 m/s.

    Then the Falcon 9 first stage could serve as a proof of principle SSTO on the switch to the Merlin 1D engine.


    Bob Clark
    If you use both the most weight efficient structures and the best sea level-to-vacuum efficient engines at the same time,
    then what you will wind up with will be a SSTO whether you intend it to or not.
    Blog: http://exoscientist.blogspot.com

 

 
Page 3 of 4 FirstFirst 1234 LastLast

Similar Threads

  1. The Coming SSTO's.
    By RGClark in forum General Astronomy Forum
    Replies: 0
    Last Post: 07-17-2011, 08:36 PM
  2. arthur c clarke's banyan trees on mars
    By vmpolesov@gmail.com in forum Amateur Astronomy Forum
    Replies: 7
    Last Post: 03-19-2007, 12:37 AM
  3. Arthur C. Clarke's 86th B'Day
    By Michael Gallagher in forum Space Exploration History Forum
    Replies: 0
    Last Post: 12-16-2003, 03:39 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBulletin® Version 4.2.0
Powered by vBulletin®
All times are GMT. The time now is 08:23 PM.