Comments for Jochen Schischka

Comment on Hello world! by Markus Schiller

Markus Schiller — Fri, 11 Mar 2011 19:16:11 +0000

With superheated air beyond 5,000 °F / 3,000 °C entering the wing, even a Cessna might be in trouble…

See CAIB Report Volume I August 2003, p.69 and p.71

Comment on Hello world! by Jochen

Jochen — Thu, 10 Mar 2011 20:09:30 +0000

Hey, you’re right, thanks for the correction!
I somehow had mixed that up with the height at foam-impact; Let’s assess this as a valuable lession in another vital discipline in addition to healthy skepticism: fact-checking.

Although, this makes understanding the Columbia break-up rather less trivial, since the ram air pressure at that height (air density: 0.0003kg/m³) and speed (5933m/sec) would roughly correspond to only 334km/h aka 208mph aka 180kts, and even the ubiquitous Cessna typically won’t come apart at comparable speeds, either; Yet, i’ve omitted stagnation temperature, or that this is hyper-, not subsonic (i hope you understand that i’d like to avoid the associated five-fold-integral exercise in this context – after all, the original statement was only meant as an illustrative subordinate clause)…

Comment on Hello world! by George William Herbert

George William Herbert — Wed, 09 Mar 2011 22:09:00 +0000

Jochen, the Columbia breakup was at 200,000 ft / Mach 19 (60 km) not 60,000 ft.

CAIB Diag. 2.6.1, pp 40-41 (position 1 second prior to loss of signal was 200,861 ft altitude, 12,384 mph)
CAIB Ch. 3.7, pp 73 and elsewhere “200,000 ft and mach 19″

Comment on Hello world! by Amir

Amir — Wed, 09 Mar 2011 19:26:44 +0000

Thanks Jochen,

“Let’s wait and see what ‘Safir Rasad’ will actually look like in the end.”

BTW, the interesting one should be Safir-e-Fajr (Safir-1B) as Fajr satellite is the heavy one. Rasad is about the same mass as Omid satellite, hence, Safir-1A will be used for its launch.

Comment on Hello world! by Jochen

Jochen — Wed, 09 Mar 2011 18:52:19 +0000

You mention an interesting example.
If i take a closer look at the LR-87-3 (Titan-I, LOX/RP-1) and the LR-87-5 (Titan-II, NTO/Aerozine-50), then i find it difficult to not see all the obvious differences – exactly confirming my argument. Compare for example the turbopump exhaust lines (long vs. short), or the exact installed location of the turbopumps (higher up vs. lower down), or some piping details (e.g. slightly slant vs. level lines to the chamber heads), or the nozzle extensions, etc., etc., etc. (BTW, irritatingly, there seem to exist some not-too-expertly improvised museum exhibits which apparently got cobbled together from LR-87-5 turbopump assemblies and LR-87-3 thrust chambers, inconclusively marked ‘LR-87′…).
Oh, and please don’t overrate the experiments of some ‘alternative space’ activists in this regard – at least it would be nice to include a mention of the results of those experiments, which typically aren’t that favorable (yeah, i know, that’s usually omitted by the guys who want to sell their stuff)…
Nonetheless, exchanging propellants normally requires at a very minimum a different turbopump and gas generator and a new injector plate (usually different optimum mixture rate, different densities, different viscosities etc. etc. etc.), even in case of ablatively cooled nozzles (and we’re talking about reactive cooling in this context, which makes matters even more complicated, as you’ve noted absolutely correctly yourself). Mark that i don’t say that this is impossible – only that this would with considerable certainty produce visible differences compared to the original (or, alternatively, results in vast performance losses and unforseen problems within other unforeseen problems).

Comment on Hello world! by Jochen

Jochen — Wed, 09 Mar 2011 17:54:42 +0000

First of all, welcome to this thread.
Back to business: The ~22t-, maybe even 23t-figure is my own estimate, based on photo-measurements (which tell me that at an l/d of ~17-17.5 and an assumed diameter of 1.25m, the official figure of 22m length is approximately correct, maybe even lightly rounded up). This is what i get with an average density of ~0.85kg/dm³ (since the payload section will be rather lightweight, plus aluminum instead of steel for the tanks plus smaller fins plus an additional mostly empty interstage section, i expect Safir to have similar overall density as Scud-B despite common-bulkheads aka no intertank sections on both stages) and a volume of approximately 26-27m³ (simple mathematics). 26t would be too dense (at an average of 0.96-1.00kg/dm³!) for a liquid-propelled missile in my eyes (even highly compacted submarine systems which e.g. mount the main engines inside of the tanks typically don’t exceed 0.91-0.94kg/dm³ – less dense than the surrounding sea water).
Additionally, the longer i’m trying to reconcile 32 tons sea level thrust with the given Safir/NoDong-engine geometry, the less consistent this looks to me (not to speak of 37 tons!). I’m beginning to suspect if this figure perhaps referred to the combined thrusts of lower and upper stage engines together (~27-28t s.l. + ~4t vac.). See my comments in answer to ‘Pedro’ – ‘claims’ are always problematic and thus should be handled with a not too small grain of salt. It’s always better to retrace the official figures based on photographic or other evidence (a classical example: if i’d blindly believe most t.v.-’documentaries’, then the Columbia broke apart at a height of 60 kilometers – a look into the CAIB Final Report tells me that these were actually 60000 feet, not meters – just as i had suspected from the start).
Let’s wait and see what ‘Safir Rasad’ will actually look like in the end.

Comment on Hello world! by Amir

Amir — Wed, 09 Mar 2011 04:43:33 +0000

I am glad that the rocketry section is back. I was one of the fans of the rocketry articles.

On another note, you mentioned a 22 tons weight for Safir SLV. Is this weight your estimation or it is from a different source? All sources I remember mentioned 26 tons weight for Safir. 32t thrust would be consistent with 26t weight and the photographic evidence. What do you think?

Comment on Hello world! by George William Herbert

George William Herbert — Wed, 09 Mar 2011 00:18:56 +0000

It’s not always true that propellant changes require significant changes in the engine justifying a new designation. The LR-87 on the Titan went from LOX/Kerosene (Titan I) to MON/Aerozene-50 (Titan II and beyond). A number of more recent aerospace startups have run the same engine on kerosene and isopropyl alcohol and other fuels; one of them was converted with intermediate efforts to liquid methane (I can’t quote the precise changes on that one).

In particular, MON and IRFNA (or for that matter, IWFNA) are mostly a materials compatibility issue. The acids are denser, slightly.

Changes that would matter most would be in the behavior of the cooling propellant, for cooled chamber motors (most, but not all – ablatives were out there until recently on Delta’s upper stage, are still on Kestrel, etc). Heat capacity going down or boiling behavior changing a lot would be potentially catastrophic, obviously, though there are tricks to handle that to some degree without complete redesign.

Comment on Hello world! by Jochen

Jochen — Tue, 08 Mar 2011 13:31:52 +0000

You’re welcome – i hope i’ll succeed in providing a little food for thought from time to time…

Comment on Hello world! by Hairs

Hairs — Mon, 07 Mar 2011 16:13:16 +0000

Hello Jochen – I just wanted to say thank you for agreeing to provide rocketry coverage on ACW.

In the past I always read both Geoff’s posts and your comments with great interest, and I’m looking forward now to seeing your thoughts on the latest in the proliferation of rocket technology.