Newsgroup: it.scienza.astronomia
Titolo: Esplorazione Planetaria 2004

Mentre ancora ci si leccano le ferite della probabile perdita del Beagle 
2 (un ottimo esempio di come NON si progetta una sonda spaziale), vi 
segnalo i tanti appuntamenti dell'esplorazione del sistema solare 2004:
2 gennaio: Stardust sorvola la cometa Wild 2
4 gennaio: Il rover americano Spirit atterra su Marte
24 gennaio: Il secondo rover Opportunity atterra su Marte. Non per 
menare gramo, ma secondo me le probabilita' che sia Spirit che 
Opportunity atterrino con successo sono piuttosto basse...
26 febbraio: Lancio della sonda Rosetta su un Ariane 5 alla volta della 
cometa Churyumov-Gerasimenko che raggiungera' nel 2014
11 maggio: Lancio della sonda Messenger su un Delta 2 alla volta di 
Mercurio. Entrera' in orbita nel 2009
1 luglio: Cassini entra in orbita attorno a Saturno
8 settembre: Genesis abbandona la sua posizione tra la terra e il sole 
per riportare a terra campioni del vento solare
17 dicembre: Huygens si separa da Cassini prima dell'atterraggio su 
Titano (gennaio 2005)
30 dicembre: Lancio di Deep Impact su Delta 2 verso la cometa Tempel 1 
che raggiungera' il 4 luglio 2005.
Inoltre da segnalare: possibile lancio della prima missione lunare 
privata TrailBlazer e i primi sorvoli lunari della SMART-1 verso la fine 
dell'anno.
-- 
To answer, replace "vizzavi" with "tiscali"
Per rispondere, sostituite "vizzavi" con "tiscali"
Pour me répondre, substituez "vizzavi" avec "tiscali"

 ha scritto nel messaggio
news:bsn1m3$js9$1...@lacerta.tiscalinet.it...
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Ti ringrazio per averci rammentato quali sono le prossime missioni spaziali
in programma.
Vorrei pero' chiederti due cose:
1) Ci descrivi qual'e' il modo GIUSTO di progettare una sonda spaziale in
modo che abbia il 100% di probabilita' di successo?
2) Quali elementi hai per supporre che le probabilita' di  Spirit ed
Opportunity di ammartare siano scarse? Spero che tu  non sia stato
contagiato dalla sindrome di asps, la quale, com'è noto, provoca uno
sfrenato desiderio che ogni missione spaziale si risolva in un fallimento.
Antonio Zanardo

 Opportunity di ammartare siano scarse? Spero che tu  non sia stato
Orreeeeeeendo!! AMMARTARE?????? :-) Passi "allunaggio", ma mica conieremo un
nuovo termine ogni volta ke approderemo su un nuovo pianeta? "Aggiovare"?
"Annettunare"?? "Applutonare"??? "Ammercuriare"????
"Atterrare" mi sembra l'ideale per tutti i pianeti, e anche per la Luna!!
Ciao!!
Xander

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Rispondo velocemente: come hanno scritto alcuni esperti esterni chiamati 
a valutare il progetto del Beagle, esso e' "solido ma marginale", nel 
senso che, per esempio, nessuno aveva mai provato il collegamento con 
l'orbiter Mars Odissey prima d'ora e che addirittura, il sito di 
atterraggio si trova in una depressione per avere un paio di km di 
atmosfera in piu' per frenare... senza contare poi che il sistema di 
atterraggio e' estremamente semplificato e non di arrivare a terra con 
velocita' ancora piuttosto alte.
Per quanto riguarda Spirit e Opportunity, e' opinione corrente che il 
periodo di sviluppo (poco piu' di due anni) sia stato troppo breve, e 
restano ancora molte incognite. Per esempio, il sistema di atterraggio 
e' stato sostanzialmente riprogettato poco piu' di un anno fa...
Paolo
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Per chiarire il concetto vi allego questo interessante articoletto:
------------------
Beagle 2 Team
Planetary and Space Sciences Research Institute
The Open University
Milton Keynes, U.K.
28 December 2003, 15:45 GMT
Communication Strategy of the Beagle 2 "Think Tank"
As part of the Media update on 27th December, Professor Alan Wells 
(Lander Operations Control Centre, University of Leicester) outlined 
details of the work being undertaken by the Beagle 2 team to assess the 
current situation. A specialist team, titled the "Analysis and Recovery 
Think Tank", has been established to concentrate on understanding the 
reasons for Beagle 2's apparent failure to make contact with Earth, and 
to address the steps that may be taken to resolve these problems.
During the media briefing Professor Wells took time to explain the 
precise nature of the earlier attempts to make contact with the 
spacecraft, and detailed the remaining opportunities as follows:
A series of 15 scheduled communication sequences were programmed into 
Beagle 2's software prior to its separation from Mars Express on Friday 
19th December. Routine communication with Mars Express before the 
separation confirmed that these commands had been successfully uploaded 
to the lander.
After touchdown the planned communication sessions should have 
automatically been triggered, by the onboard 'clock', to correspond with 
the known passing of the orbiting spacecraft Mars Odyssey (NASA), and 
later on in the mission, Mars Express (the ESA 'mother ship'). A number 
of the pre-programmed sessions were also scheduled to correspond with 
times when the landing site is in 'sight' of the Jodrell Bank Radio 
Telescope. Any signal picked up by Jodrell, or an alternative telescope, 
will only serve to confirm the well-being of Beagle 2 -- it does not 
offer an opportunity for two-way communication; this can only be 
achieved via Mars Odyssey or Mars Express.
If the lander software is running as planned, and according to the 
initial timing dictated by the onboard clock, a number of the programmed 
communication sessions have already passed.
Sessions 1 and 3 (between 04:54 and 06:14 on Christmas Day morning and 
between 17:33 and 18:53 on Boxing Day evening respectively) both 
occurred during the martian night, and were intended to open 
communication with Mars Odyssey. In the planned communication sessions 
with an orbiting spacecraft, Beagle switches into 'listening' mode for 
80 minutes. During the pass over the landing site Mars Odyssey will send 
out a series of 'hails' which, if picked up by Beagle, will enable the 
lander's receiver to lock onto the signal from the orbiter and activates 
the lander's transmitter and communications can proceed (any reply from 
Beagle would be 'headed' up with the call sign composed by Blur).
No response was received by Mars Odyssey to indicate that the 'hail' 
messages had reached Beagle 2 during either of the above sessions.
When a planned communication session is intended for reception by the 
Jodrell Bank radio telescope, Beagle 2 is configured to send a repeating 
unmodulated signal, transmitting for 10 seconds then remaining inactive 
for 50 seconds, for a duration of 80 minutes.
Sessions 2, 4 and 6 (between 22:20 and 23:40 on Christmas Day evening, 
between 23:00 and 24:20 on Boxing Day night and between 22:56 and 00:16 
27th December respectively) coincided with opportunities to view the 
surface of Mars with the Jodrell Bank radio telescope. Unfortunately no 
signal was detected by the giant telescope.
Session 5 (between 6:17 and 7:37 on the morning of 27th December) 
occurred during the martian day, and Beagle 2 should have again been in 
its 'listening' mode at a time when Mars Odyssey was passing over the 
landing site. Sessions occurring in the martian daytime differ from 
those occurring during the night as Beagle would automatically send any 
stored data when sunlight is available to charge the battery. Beagle is 
programmed to 'concentrate' on receiving data at night time to avoid 
draining the battery with power intensive data transmission.
However, again the telemetry returned by Mars Odyssey to Earth did not 
contain any evidence of communication between the orbiter and lander.
The remaining scheduled communications sessions are as follows:
Sessions coinciding with Mars Odyssey pass:
* Session 7 -- 28/12/03 (18:57 - 20:17 GMT)
* Session 8 -- 29/12/03 (07:41 - 09:01 GMT)
* Session 9 -- 30/12/03 (07:24 - 08:44 GMT)
* Session 10 -- 30/12/03 (20:20 - 21:40 GMT)
* Session 11 -- 31/12/03 (09:04 - 10:24 GMT)
Please note that any signal from Beagle 2 (either directly to the 
Jodrell Bank radio telescope or via an orbiting spacecraft) will take at 
least 9 minutes to reach earth, owing to the vast distance that it must 
travel.
One possible explanation that has been raised for the apparent silence 
is the potential for incompatibility between the systems on board Beagle 
and those used by Mars Odyssey. The Beagle team has been in constant 
contact with the Jet Propulsion Lab, in Pasadena, and fellow scientists 
there are presently checking through data and records in order to 
ascertain whether there may be any problems with the transmitters and 
receivers aboard Odyssey. It is important to note that neither of the 
communication routes attempted so far has ever been tested, therefore it 
is possible that the best opportunity for successful communication may 
arise when Mars Express achieves its final orbit and can take part in 
the search for Beagle.
A backup has been built into the communication schedule such that if 10 
scheduled sessions pass unsuccessfully then Beagle 2 will switch to an 
emergency mode 'search mode 1'. Planned Jodrell contact sessions are 
included in the count because Beagle can have no way of knowing whether 
these 'one-way' sessions have been successful. When the lander switches 
to search mode 1 it will proceed to attempt a communication with the 
best daytime and best nighttime orbiter pass each day -- these times are 
calculated according to an onboard model of the orbits of both Mars 
Odyssey and Mars Express.
Session 10 is scheduled for the evening of 30th December, and if a 
regular contact has not been made by this time 'search mode 1' will be 
activated, increasing the opportunity for communication with a 'passing' 
orbiter or for detection of Beagle 2 by radio telescope from Earth.
If a further 10 communication sessions are unsuccessful, Beagle will 
then switch to 'search mode 2'. The second emergency mode involves the 
production of a signal throughout the martian day (power is still 
conserved during the night). With two 'search mode 1' sessions taking 
place each day, the adoption of search mode 2 would, in theory, begin on 
January 5th -- soon after the date when Mars Express is first available 
for communication.
A further explanation for the lack of contact between Beagle and the 
Earth is that the onboard clock may have been corrupted during the 
entry, descent, and landing stage of the mission. If this is indeed the 
case, the above scheduled communication sessions may not have 
corresponded accurately with the passage of Mars Odyssey over the 
landing site or with the viewing windows afforded to the Jodrell Bank 
telescope. It is possible that Beagle 2 is signalling correctly but not 
at a time when Mars Odyssey is passing or when Jodrell Bank can 'see' 
Mars. Consequently, when Beagle assumes 'search mode 1' and begins 
signaling more regularly it may be possible for Odyssey or Jodrell to 
pick up the 'additional' transmissions.
In addition, a further radio telescope at the University of Stanford, 
California will begin the hunt for a signal from Beagle 2 the evening of 
27th December. The telescope at Stanford has a viewing window that is 
one hour longer than that afforded to Jodrell Bank -- therefore the 
opportunity for a signal to be picked up, if it is being transmitted at 
an unexpected time, will also be increased. The Stanford telescope has 
previously been used to monitor faint sources of radiation in deep 
space. Consequently it is thought that there may be some potential for 
it picking up other indicators of activity on Beagle besides the 
expected transmitter signal. The onboard processors will produce low 
levels of radiation that may be weakly 'visible' to the telescope -- 
this might be considered comparable to looking for signs of Beagle's 
'heartbeat', rather than listening for its 'bark'! It was, however, 
noted that these systems on Beagle have been shielded to protect them 
from sources of external radiation hence any signal from this internal 
source may be extremely small. Radio telescope scientists have special 
ways of distinguishing small signals from other background 'noise'.
Members of the Beagle 2 team are also exploring the possibility of 
'recruiting' other radio telescopes to hunt for the signal from Mars. A 
telescope on the other side of the Earth would allow the search to 
continue at different times. It is understood that staff at the Parkes 
telescope (Sydney, Australia) are investigating whether they have 
appropriate detection equipment to look for Beagle 2.
Whilst it may not be possible to establish two way communications with 
Beagle 2 via a radio telescope it will aid the team to pinpoint the 
lander's location, and provide a time reference point. If the onboard 
clock has been corrupted it is likely to affect the absolute timing of 
the communication windows rather than the relative timing.
In order to address the potential problems associated with an incorrect 
clock setting on Beagle 2, a 'blind command' was transmitted by Mars 
Odyssey during the pass over the landing site yesterday morning 
(27/12/03 - session 5). The hope is that Beagle may be able to receive 
such signals, but is not currently able to transmit. The effect of this 
command would be to reset the onboard clock with the aim of 
resynchronising the process and prompting an opportunity for successful 
communication.
'Blind commands' can also be used by the 'Lander Operations Control 
Centre' (LOCC) to control other processes onboard Beagle 2, without the 
requirement for two-way communication. Commands to control the motors 
operating the central hinge, or the hinges controlling the solar arrays 
may be sent via Mars Odyssey or Mars Express to affect some minor 
repositioning of the lander -- this approach may be used to correct any 
potential problems that might have occurred with the opening of the 
arrays, or if the lander is inappropriately positioned, for example, 
leaning at a restrictive angle against a rock.
Such a strategy is not without considerable risk because any command may 
impact other processes taking place on the lander. It is also very 
difficult to command a spacecraft without any information about its 
current status -- imagine trying to drive a radio-controlled car around 
a track without being able to see or hear the movement, or even know 
what the track looks like! The LOCC team will be able to make a risk 
assessment by testing the implication of any proposed activity on a 
working replica of the Beagle lander in their control centre at the 
University of Leicester.
Finally Professor Wells reassured the gathered media that the team were 
still in good spirits, and dedicated to the challenge ahead -- and 
promised that, "We'll keep going until every possibility has been 
exhausted".
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Ciao Antonio :-)
A parte il fatto di far atterrare una sonda dentro degli airbag(ok al
pathfinder č andata bene)che puo essere discutibile;il problema secondo me č
che con questo metodo ci sono troppe variabili.Oltre al fatto che non sai
mai dove "cadrą".Non ha molto senso ,secondo me,spendere tanti soldi senza
sapere dove finirą la sonda;ci sono piu probabilitą che non atterri nel modo
giusto che il contrario.
La strada da intraprendere ,secondo me,č ben diversa,e cioe progettare sonde
"guidabili"e non lasciate al proprio destino.So che ci vogliono piu soldi,ma
almeno sģ č piu sicuri che atterri sana e salva.
Saluti
Franci michele
PS.leva NONSPAM per rispondermi


Dunque si tende a dare la colpa ad un problema di comunicazione (la cosa
sarebbe abbastanza imperdonabile...)
Io piuttosto mi chiedo se non sia un problema di atterraggio dal momento che
delle sonde dotate di sistema ad airbag se n'č salvata solo una. Ho
confrontato velocemente i dati di discesa delle sonde Viking con quella del
Beagle 2 ed ho notato che nella sostanza sono simili nel tratto iniziale,
tranne il fatto che il Beagle ha espulso il paracadute principale a piů di
7km di altezza mentre le Viking a 6km. Ovviamente le sonde dotate di airbag
devono aprirlo prima per diminuire la velocitŕ di impatto, e cosě quando č
stato aperto il paracadute, il Beagle viaggiava a 1100 km/h, cosa che sulla
Terra sarebbe impensabile, ma che sulla rarefatta atmosfera marziana non dŕ
grossi problemi. Il dubbio che mi viene č questo: č stato considerato
l'effetto di polveri in sospensione? La debole gravitŕ marziana associata a
forti venti potrebbe alzare polveri a qualche km di altezza (da notare che
due giorni prima dell'atterraggio vi fu un alert per una possibile tempesta)
e l'effetto abrasivo suběto dai paracadute potrebbe essere stato fatale.
Nelle missioni Viking questo effetto di "sabbiatura", č stato suběto per un
tempo minore e velocitŕ minori mentre per la Pathfinder l'intensitŕ della
sospensione potrebbe essere stata fortunatamente bassa, tale da poter
consentire un atterraggio corretto. Che ne pensi?