Hot answers tagged

13

Yes, the pressure of the first stage exhaust is always at least slightly subatmospheric, because that gives the maximum average ISP over the whole burn time. Rockets with boosters attached (parallel staging) often operate at the lowest possible exhaust pressure that prevents the flow from detaching from the nozzle walls. Historically, the Summerfield ...


11

A document from NASA Safety & Mission Assurance suggests the reason is structural: Thin-­skinned Centaur cannot easily support the giant 5.4 meter diameter payload fairing, so the Contraves composite fairing also encloses Centaur. My first guess, however, was aerodynamics, particularly the Whitcomb area rule: for transonic flight, abrupt changes of ...


11

The main engine on the Atlas, as with most orbital launchers, is gimballed such that it can direct thrust to offset the imbalanced thrust from the boosters (or any other disturbance). Atlas uses only as many boosters as it needs for a given payload -- from zero to 5 -- and some of those configurations are asymmetrical. It looks especially odd using only a ...


10

BODA appears to stand for "burn-out detection algorithm". During the launch of an Atlas V equipped with solid rocket boosters, the main engine throttles down after about 75 seconds to limit g-force. Once the burn-out of the solid rockets is detected, the main engine throttles back up to 100%. I'm not sure if the algorithm is based on determination of ...


10

That's a hydrogen vent fin disposing of GH2 (gaseous hydrogen) that can outgas into the payload fairing from the Centaur upper stage's LH2 (liquid hydrogen) tank that is stored in a balloon tank at the top of the upper stage. From History of the Titan Centaur Launch Vehicle (PDF):     This liquid hydrogen leakage caused explosion of the ...


9

Old school Atlas -- 0.1 to 0.4 inches (2.5 to 10 mm) thick -- so, actually, similar to the metal portion of the shuttle ET. Centaur upper stage tanks -- 0.014"--0.016" (0.36 to 0.41 mm) thick (!). Saturn V's 1st stage tanks varied in thickness from 0.170"-0.254" (4.32 to 6.45 mm).


9

Centaur upper stages have a Propellant Utilization (PU) system. While this document is old, the fundamentals apply. To realize optimum performance in a liquid-fueled bipropellant space vehicle, it is necessary to control both propellants so as to deplete them simultaneously. Such a simultaneous depletion both minimizes ...


8

From perusing online, it seems there's a consensus that the insulating foam is just that color. They painted the Delta II, but stopped painting due to the added weight. As to why they painted the Delta II (and Saturns), I believe it is for protection against UV. They probably solved the UV issue, and thus opted for the lower weight for the Delta IV.


7

There are tradeoffs at work here. The current configuration allows them to use one first stage design for 1-5 boosters. A first stage that has symmetric attachment points, needs 2+4+4 = 10 attachment points for the 2, 3, 4, and 5 booster cases. Another approach would be to discard the odd numbered configurations altogether and go to 2, 4, 6, 8 boosters. ...


6

SLC-40 and 41 are neighbors, no other pads in between. Some debris landed further away than SLC-41. They share some systems, e.g. the deluge system. The only good source I've found is this post by a member of the emergency response team. On Sept. 1, OSIRIS-REx was still in the vertical integration building next to the launch pad. The explosion ...


6

Adding to Russell's answer, Falcon 9 apparently has 3/16''-thick walls (4.7mm). This is interesting, because it's more than Shuttle's ET and about as much as parts of S-IC, despite being a smaller rocket. Presumably this is for extra structural margins to make the stage survive multiple reuse.


6

According to Wikipedia, RD-180 has only been used on the Atlas line, so I would assume they're talking about the track record of the whole RD-170 family -- the Energia and Zenit applications in particular.


6

You can find lots of information in the User Guide (420-page PDF). Page 57 shows the performance effects: Atlas V 400 series performance is based on the use of the 4-m EPF. GTO performance with the LPF is approximately 35 kg (77.2 lb) more than the EPF with the 401 configuration and 44 kg (97 lb) more with the 431 configuration. GTO performance with the ...


6

Yes, however the decision to launch the mission on Atlas V was made years ago, and it is impossible to change now that the launch is less than a month away. InSight is estimated to weigh 360 kg. Falcon 9 has a payload capacity of 4,020 kg to Mars. The most likely reason for choosing Atlas V over F9 is most likely the history of the mission. InSight's ...


5

If it's a rocket launch, happens at around engine ignition, and it sounds like some variation of 'whooop', you can bet it's the sound of turbomachinery very rapidly spooling up. Consider those turbopumps go from zero to tens of thousands of RPMs in fractions of a second, they cover the whole range of audible frecuencies, fast. I actually ended here while ...


5

You're forgetting that on top of their mass being different, larger ø also means larger cross sectional area, and with it increase in aerodynamic drag. So larger ø ones are heavier, subject to stronger atmospheric resistance, have larger contact area subjected to ascent heating, and with a more contoured launch vehicle's body deviate from ideal aerodynamic ...


5

Satellites are finely tuned to work in a specific environment. Space is a tough environment, but usually pretty consistent. One of the things required is to keep the spacecraft at a certain operating temperature at all times, including on the ground and on the rocket. There are a few components that are particularly sensitive, most notably the batteries. ...


4

Since 2004, it's been policy of the US government to assure there are at least two launcher families available for launching "national security payloads" (e.g. military surveillance and communication satellites). Prior to the entry of Antares and Falcon 9 in the market, this pretty much meant Atlas and Delta, therefore USAF was required to make the necessary ...


4

The goals of Assured Access to Space are (PDF of a hearing by the House Committee on Armed Services, page 14): The existing policy, codified in federal law, requires that assured access policy and spending, at a minimum, achieve the following two objectives: the availability of at least two space launch vehicles (or families of space launch ...


4

I did some searching. Russell's comment provides the only theory I've found: LM had Atlas III and Titan IV. Atlas V as a follow on to both and since it incorporated elements of each, so did the name. It was called Atlas because it was an Atlas: same 10' dia Centaur, same fairing, same avionics (Centaur controls the whole vehicle), same first stage ...


3

Since we know the Centaur on Atlas 5 uses RL10C engines, we can look that up. The current RL10C engine mixture ratio is 5.5.


3

The short answer is that the Isp of the Falcon's RP-1/LOX upper stage engines is much less than the Atlas V's LH/LOX. The primary metric of interest is $\Delta v$, which depends on $I_{sp}$ and mass fraction. If you need more $\Delta v$ for a particular mission, but your $I_{sp}$ is lower than another rocket's, that means you'll need a better mass fraction, ...


3

The Delta rocket started out with separate versions of the aft end for different numbers solid rocket boosters attached. Eventually McDonnell Douglas standardized, introducing the Universal Boattail Thor (UBT) with with a full complement of nine attach points regardless of how many solid boosters were to be flown on a mission. The positions for the boosters ...


3

The design of the Delta 4 is such that each CCM (Common Core Module) has fittings to support thrust through the strap on mount points. It has to support 2 other CCMs attached for the Delta Heavy model, and then lower mount points for the various combinations of SRBs. For some reason I do not fully understand the Delta 4 pays a heavier price in terms of both ...


3

While other answers are perfect from an engineering point of view, there is another aspect. The 4m and 5m fairings have different designs and are produced at different sites. 5m fairings have aluminum honeycomb core and graphite epoxy face panels and are made in Emmen, Switzerland (RUAG), the same manufacturer that makes Ariane 5 PLFs. Basically, this is a ...


2

Per Spaceflight101, the Atlas 401 has a mass at launch of 334.5 tons (this likely varies with fuel load) and thrust is 3827kN. Cygnus is "just over 8 tons"; GPS IIF is 1.63 tons. So for the GPS IIF launch, we have $\frac{3827}{334.5+1.63} = 11.38 m/s^2$ acceleration, less Earth's gravity of $9.81 m/s^2$, gives acceleration off the pad of $1.57 m/s^2$. ...


2

As detailed in this other answer, they provide noise dampening. Thanks to Hobbes who is possibly a Helmholtz nut. ;) (...gotta wait 2 days before I can close this question...)


1

An estimate from 2016 has the mass budget at 5000 kg. Curt Niebur, outer planets program scientist at NASA Headquarters, said at the meeting that the biggest challenge of adding the lander to the Europa mission is its mass: about 8,000 kilograms, to accommodate the propellant needed to land the spacecraft softly on the surface. He added that estimate was ...


1

For ariane 5 the thickness is: 8mm for the solid boosters 4mm for the cryogenic main stage. However both have an additional thermal insulation layer. I couldn't find data for the booster [see comments], but it's 2cm for the cryogenic one. Considering this data I wouldn't be surprised if the insulating layer is missing from the other answers. PS: the ...


1

Arianespace offers secondary payload space on both Ariane 5 and Vega. Their earliest 'microsatellite' launch was using the ASAP structure on an Ariane 40 on January 22, 1990. The Ariane 5 can launch 2 large satellites using the SYLDA (SYstème de Lancement Double Ariane) fairing. Also for the Ariane 5, the Ariane Structure for Auxiliary Payloads (ASAP) is ...


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