- 8 - LSDS-1574
Version 5.0
Section 2 Observatory Overview
The L8 Observatory is designed for a 705
kilometer (km), Sun-synchronous orbit, with a
16-day repeat cycle, completely orbiting the
Earth every 98.9 minutes. S-Band is used for
commanding and housekeeping telemetry
operations, while X-Band is used for instrument
data downlink. A 3.14 terabit SSR brings back
an unprecedented number of images to the
USGS EROS archive.
L8 carries a two-sensor payload: the OLI, built
by BATC, and the TIRS, built by NASA GSFC.
Both the OLI and TIRS sensors simultaneously
image every scene but are capable of
independent use if a problem in either sensor
arises. In normal operation, the sensors view
the Earth at-nadir on the Sun-synchronous
Worldwide Reference System 2 (WRS-2)
orbital path/row coordinate system, but special
collections may be scheduled off-nadir. Both
sensors offer technical advancements over earlier
Landsat instruments. The spacecraft, with its two
integrated sensors, is referred to as the L8 Observatory.
2.1 Concept of Operations
The fundamental L8 operations concept is to collect, archive, process, and distribute
science data in a manner consistent with the operation of the L7 satellite system. To
that end, the L8 Observatory operates in a near-circular, near-polar, Sun-synchronous
orbit with a 705 km altitude at the Equator. The Observatory has a 16-day ground track
repeat cycle with an equatorial crossing at 10:11 a.m. (+/−15 min) Mean Local Time
(MLT) during the descending node. In this orbit, the L8 Observatory follows a sequence
of fixed ground tracks (also known as paths) defined by the WRS-2. The L8 launch and
initial orbit adjustments placed the Observatory in an orbit to ensure an 8-day offset
between L7 and L8 coverage of each WRS-2 path.
The Mission Operation Center (MOC) sends commands to the satellite once every 24
hours via S-Band communications from the Ground System to schedule daily data
collections. Landsat 8 Long-Term Acquisition Plan (LTAP-8) sets priorities for collecting
data along the WRS-2 ground paths. LTAP-8 is modeled on the systematic data
acquisition plan developed for L7 (Arvidson et al., 2006). OLI and TIRS collect data
jointly to provide coincident images of the same surface areas. The MOC nominally
schedules the collection of 400 OLI and TIRS scenes per day, where each scene
covers a 190-by-180 km surface area. The objective of scheduling and data collection is
to provide near cloud-free coverage of the global landmass for each season of the year.
Figure 2-1. Illustration of
Landsat 8 Observatory