Space Technology

Bank exams love testing the same skill in two different costumes — and the SBI PO Number Series section has a favourite trick. Once you have figured out the rule of one series, the very next question hands you a second series that starts with a new number but follows the exact same rule. The candidate who hunts for a brand-new pattern wastes 90 seconds. The candidate who recognises the format finishes both questions in under a minute.

Definition: The Second-Question Pattern is an SBI PO number-series format where a complete sample series is given (so its rule can be cracked), followed by an incomplete series that begins with a different first term but obeys the same arithmetic rule. You are then asked for a specific position (typically the 3rd, 4th or 5th term).

Why This Format Exists

The examiner is not testing whether you can crack two patterns. They are testing whether you can transfer a rule from one starting point to another and whether you can correctly count steps. Both are bread-and-butter banking skills — applying the same EMI formula to different loan amounts, applying the same depreciation rule to different machines. The number-series wrapper is just dressing.

The Core Method

The technique is brutally simple in three moves:

Step 1 — Read the sample series end to end and extract the rule. Is each term the previous one + n, x n, ^2, or a chain like x2 + 1, x3 + 2, x4 + 3? Confirm the rule by checking it across at least two consecutive jumps in the sample.

Step 2 — Take the new first term from the question series. Do not borrow the original first term. This is where most students lose marks: muscle memory pulls them back to the sample's starting number.

Step 3 — March the rule forward the required number of steps. Compute term by term, writing each on the rough sheet so you do not lose count. Stop at the asked position.

Memory aid: "Learn the rule, change the seed." The plant grows the same way, but it sprouts from a different seed.

Counting Steps Correctly

This is the silent killer of the format. "Find the 3rd term" does NOT mean apply the rule 3 times. The first term is given. Reaching the 2nd term takes 1 application. Reaching the 3rd term takes 2 applications. In general:

To reach the nth term from the first term, apply the rule (n - 1) times.

A small table makes this unforgettable.

:::compare

Why it matters: One miscounted step turns a correct rule into a wrong answer, and the wrong answer is always sitting there as a distractor in the option set. The examiner deliberately places the off-by-one number among the four options.

Worked Example

Question:
Sample series: 3, 7, 15, 31, 63, 127
New series first term: 5. Find the 3rd term.

Solution:
Step 1: Find the rule from the sample. 3 -> 7 (x2 + 1), 7 -> 15 (x2 + 1), 15 -> 31 (x2 + 1). Confirmed: each term = previous x 2 + 1.
Step 2: Take the new first term = 5. Apply the rule (3 - 1) = 2 times to reach the 3rd term.
Step 3: 1st application — 5 x 2 + 1 = 11. So the 2nd term = 11.
Step 4: 2nd application — 11 x 2 + 1 = 23. So the 3rd term = 23.
Conclusion: The 3rd term of the new series is 23.

Real-world example: Imagine a fixed-deposit scheme that doubles your money each year and adds Rs 1 as a loyalty bonus. If Aman starts with Rs 3 and Bhavna starts with Rs 5, after the same number of years their growth rule is identical, but their balances are different because the seed amount is different. The bank question is literally this scenario in disguise.

Common misconception: "The new series must follow a new rule because the first term is different." Wrong. The whole point of the format is that the rule is shared. A different starting number does not change the multiplication, addition or chain pattern operating on it. The setter is testing rule-transfer, not rule-discovery.

Speed Tips for the Exam Hall

Because you only need 2 to 4 steps, manual computation beats calculator memory. Write the first term, draw an arrow, write the rule above the arrow, write the next term. Repeat. Even a chain rule like "x1 + 1, x2 + 2, x3 + 3, x4 + 4" can be marched out in under 25 seconds with practice.

If the rule of the sample is something complicated like differences forming a new series (e.g., differences are 4, 8, 16, 32 — themselves doubling), the same nested rule applies to the new series. The first difference is now applied to the new starting number, then the next difference, and so on. The seed changes; the engine does not.

:::keypoints

• The Second-Question Pattern reuses the rule of the sample series with a new first term.
• Crack the rule from the complete sample series, never from the incomplete one.
• For the nth term, apply the rule (n - 1) times, not n times.
• The new starting number is the only thing that changes — the operation stays identical.
• Most asked positions are the 3rd, 4th or 5th term, so 2 to 4 manual steps are enough.
• The wrong off-by-one answer is almost always one of the four options. Re-count.
• Speed comes from rough-sheet writing of each step, not from mental shortcuts.
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:::memory
"SAME ENGINE, NEW SEED." The sample teaches the engine; the question gives the seed; you drive it forward (n - 1) times. SES = Sample, Engine, Seed.
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:::recap

• Extract the rule from the sample series first.
• Apply the same rule to the new first term.
• Count steps as (n - 1) to reach the nth term.
• Manual step-by-step writing prevents off-by-one mistakes.
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Orbital velocity (to stay in circular orbit near Earth): v = √(GM/r) ≈ 7.9 km/s for LEO. Escape velocity (to break free of Earth's gravity): v = √(2GM/R) ≈ 11.2 km/s at Earth's surface. Key relation: escape velocity = √2 × orbital velocity. Escape velocity is independent of the object's mass and direction; depends on the planet's mass and radius. Memory aid: '11.2 to escape, 7.9 to orbit.' First cosmic velocity = orbital (7.9), second cosmic velocity = escape (11.2), third cosmic velocity ≈ 16.7 km/s (to escape the solar system from Earth). For the Moon escape velocity is only ~2.4 km/s due to low mass.

PSLV (Polar Satellite Launch Vehicle): 4-stage, alternating solid-liquid stages; workhorse for SSO/polar and small GEO payloads; launched Chandrayaan-1 and Mangalyaan. GSLV Mk II: 3-stage with indigenous Cryogenic Upper Stage (CUS); ~2.5-tonne GTO payload. LVM3 (earlier GSLV Mk III): heaviest, 3-stage (2 solid boosters S200 + liquid L110 core + cryogenic C25); ~4-tonne GTO / 8-tonne LEO; launched Chandrayaan-2, Chandrayaan-3, and crewed Gaganyaan. SSLV (Small Satellite Launch Vehicle): for small satellites up to ~500 kg to LEO, 'launch-on-demand.' Memory aid: cryogenic engines use liquid hydrogen (fuel) + liquid oxygen (oxidiser), giving high specific impulse for heavy GTO missions.

Chandrayaan-1 (2008, PSLV): India's first lunar mission; its Moon Impact Probe and the Moon Mineralogy Mapper (NASA payload) confirmed water/hydroxyl molecules on the lunar surface. Chandrayaan-2 (2019, LVM3): Orbiter (still functioning), Vikram lander (crash-landed), Pragyan rover. Chandrayaan-3 (2023, LVM3): Successful soft landing on 23 August 2023 near the lunar South Pole — making India the FIRST country to land near the South Pole and the 4th to soft-land on the Moon. Lander = Vikram, Rover = Pragyan; payloads ChaSTE (thermal), ILSA (seismic), RAMBHA (plasma). Memory aid: 'C-3 = South Pole, 23 Aug (now National Space Day).' Chandrayaan-1 → water; Chandrayaan-3 → South Pole soft landing.

Mars Orbiter Mission (MOM/Mangalyaan, 2013, PSLV): made India the FIRST country to reach Mars orbit on its first attempt and the first Asian nation to reach Mars; entered orbit 24 Sep 2014; notably low-cost. Aditya-L1 (2023, PSLV): India's first solar mission, placed in a halo orbit around the Sun–Earth Lagrange point L1 (~1.5 million km from Earth), giving continuous unobstructed view of the Sun. Key payload: VELC (Visible Emission Line Coronagraph) studies the solar corona. L1 is favoured because gravitational forces balance there, allowing a satellite to 'hover' with minimal fuel. Memory aid: 'Aditya = Sun god → L1 Sun-watcher.' Lagrange points: L1, L2, L3 unstable; L4, L5 stable.

Gaganyaan: India's first crewed spaceflight programme, aiming to send astronauts ('Gagannauts'/Vyomanauts) to LEO (~400 km) aboard LVM3 with indigenous crew escape system. NavIC (IRNSS): regional navigation system of 7 satellites (mix of GEO and inclined geosynchronous orbits) covering India and ~1500 km around it; uses L5 and S-band; civilian (SPS) and restricted services. GAGAN: GPS-aided augmentation for aviation. INSAT/GSAT: communication satellites in GEO for broadcasting, telephony, weather (INSAT carries VHRR/meteorological payloads). Memory aid: 'NavIC = regional GPS, 7 satellites; GAGAN = aviation booster.' Bhuvan is ISRO's geo-platform; NISAR is the upcoming ISRO–NASA radar imaging satellite.

Remote sensing acquires information about Earth without physical contact, using reflected/emitted electromagnetic radiation. Active sensors (RADAR, LiDAR) emit their own energy; passive sensors (most optical cameras) rely on sunlight. Four resolutions: (1) Spatial — smallest object detectable (pixel size); (2) Spectral — number/width of wavelength bands; (3) Radiometric — sensitivity to brightness differences (bit depth); (4) Temporal — revisit frequency over the same area. Memory aid: 'SSRT — Space, Spectrum, Radiance, Time.' Synthetic Aperture Radar (SAR) works day-night and through clouds (microwave penetrates cloud) — used in RISAT and the upcoming NISAR. India's main remote-sensing satellites: CARTOSAT (cartography/high spatial resolution), RESOURCESAT (natural resources), OCEANSAT (ocean colour), RISAT (radar).

Communication satellites sit in geostationary orbit so ground antennas can point at a fixed spot. They use transponders that receive an uplink signal, amplify and shift frequency, and retransmit (downlink). Common bands: C-band (lower frequency, rain-resistant), Ku-band, Ka-band (higher frequency, more bandwidth but rain fade). India's INSAT/GSAT series handle broadcasting, telecom, tele-education, telemedicine and disaster warning. Weather satellites are of two types: geostationary (INSAT, continuous view of one hemisphere) and polar-orbiting (global coverage, higher resolution). INSAT-3D carries an imager and sounder for atmospheric profiling. Memory aid: 'GEO for comms & continuous weather watch; Polar for global, sharper weather data.'

During floods and cyclones, SAR satellites (RISAT) map inundation even through cloud cover, while INSAT-3D tracks cyclone tracks and intensity — feeding IMD's early warnings (helping evacuate ahead of cyclones like Fani/Amphan). In agriculture, the FASAL and CHAMAN programmes use RESOURCESAT/multispectral data to estimate crop acreage and yield via vegetation indices (NDVI = (NIR−Red)/(NIR+Red); healthy vegetation reflects strongly in near-infrared). Forest cover assessment by FSI, groundwater prospecting, and the SVAMITVA scheme (drone + satellite property mapping) are other uses. Memory aid: 'Red = stress, NIR-high = healthy crop.' Bhuvan portal disseminates this geospatial data for governance.

James Webb Space Telescope (JWST, 2021, NASA–ESA–CSA): largest space telescope, observes mainly in infrared, positioned at the Sun–Earth L2 point (~1.5 million km, anti-sun side) to stay cold and shielded; successor to Hubble (which orbits Earth in optical/UV). Artemis programme (NASA): aims to return humans to the Moon, including the first woman and person of colour, and build the Lunar Gateway station. Mars rovers: Perseverance (2021, seeks signs of past life, carried Ingenuity helicopter). China's Tiangong is an operational space station; Chang'e missions explore the Moon (Chang'e-5 returned samples; Chang'e-6 returned far-side samples). Memory aid: 'JWST = infrared, L2, cold; Hubble = optical, Earth orbit.'

Space debris (defunct satellites, spent stages, collision fragments) threatens active assets at orbital speeds (~7–8 km/s). The Kessler Syndrome describes a cascading chain of collisions generating ever more debris, potentially rendering orbits unusable. ISRO's response: Project NETRA (Network for Space Object Tracking and Analysis) for debris monitoring, and the IS4OM centre; India targets a 'Debris-Free Space Missions' goal by 2030. Key treaties: Outer Space Treaty (1967) — space is the 'province of all mankind,' no national appropriation, no WMD in orbit; Moon Agreement (1979, poorly ratified); Artemis Accords (US-led principles, India signed in 2023). Memory aid: 'OST 1967 = the constitution of outer space.'

India opened space to private players: IN-SPACe (Indian National Space Promotion and Authorization Centre) is the single-window promoter/regulator; NSIL (NewSpace India Limited) is the commercial/PSU arm handling demand-driven launches and tech transfer; ISRO focuses on R&D. Indian startups: Skyroot Aerospace (Vikram-S, India's first privately built rocket, 2022) and Agnikul Cosmos (Agnibaan with 3D-printed semi-cryogenic engine). The Indian Space Policy 2023 formalised these roles and 100% FDI reforms followed. Globally, SpaceX pioneered reusable rockets (Falcon 9) and Starship; reusability slashes launch cost. Memory aid: 'IN-SPACe = promote/permit, NSIL = sell/commercialise, ISRO = research.'